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le JLitiratg

RUDIMENTARY TREATISE

OxH

'CLOCK AND WATCH MAKING:

WITH A CHAPTER ON

CHURCH CLOCKS;

AND AN ACCOUNT OP THE PROCEEDINGS RESPECTING THE GREAT

WESTMINSTER CLOCK.

\^ nnmerotis IStatomgs*

EDMUND BECKETT DENISON, M.A.,

AUTROS OF TWO PAPERS ON CWOK ESCAPEMENTS IS THE CAMBKIDGK

PHILOSOPaiCAL TBAM3ACTI0NS.

LONDON :

JOHN wIaLE, 59, HIGH HOLBOEN.

1850.

./r

T-e-C 5 ) V -b-'o

V';?/ARD UNIVERSTTY

^mvj^^L OF ENeiJEjaim'

JUN 20 1917

t • i--^* ■ 1 1

A , '

CONTKNTS.

S^CT-

PAGE

136

Frame

. 173

137

Foiar-wheeled train (drawing)

. 175

139

Three-wheeled trains ....

. 178

140

Doable frame (drawing)

. 180

141

Jack wheel for winding . . . .

. 181

142

Long barrels

. 182

143

■ Wire ropes

. 183

144

Double hammer

. 184

145

Calculation for three-wheeled trains

. 185

146

Striking part for three-wheeled train

. 186

147

Shape of crutch

. 188

148

Spring fork

. 189

149

Dial and leading-off work

. 190

Friction rollers (drawing) . . . ,

. 192

150

Adjusting work

. 193

151

Size of dials

. 196

152

Material of dials ....

. 199

153

Illuminated dials ....

. 200

155

Hands

. 202

157

Maintaining power for winding

. 204

158

Bolt and shutter ....

. 205

159

New construction of (drawing)

. 209

160

Mr. Airy's going barrel (drawing)

. 211

161

Striking part (drawing) . . . .

. 214

164

New Striking wheel (drawing)

. 218

165

Loss of power in striking . . . .

221

167

Quarters (drawing)

224

168

Chimes of St. Mar/a, Cambridge .

225

169

Bells . . . .

227

CONTENTS.

SECTION

P^GE

171

Time of striking first blow of the hour .

230

172

Bemontoire in train . . ■ .

231

173

Bojal Exchange dock remontoire (drawing) .

234

175

iVench gravity remontwe (drawing)

236

176

Bemontoire with continuous motion

237

177

Spring remontoire, Meanwood clock (drawing)

239

178

Cast iron wheels .....

245

179

Gou-metal ......

246

181

Painting and oiling

248

182

Pnllevs

249

183

Case for clock

250

184

Provision for weights falling

251

185

Proceedings respecting the great Westminster

dock

252

186

Mr. Airy's conditions .....

257

187

Pendulum accderator ....

258

188

Mr. Airy's report

263

189

On public docks in general

266

191

On specifications and tenders for docks

269

192

Church docks without dials

272

193

Advice to churchwardens ....

273

lj».e^T»1"v^<^

ERRATA.

Page 11, line 5, after ^ibr read the day before,

19, ,; 5, iot first read innermost , and for make read mark.
6, for «, read «s.

5> »>

76, „ 3, for - read -r .

„ — „ 5, for -^ read -^.

3> 77, „ 5, for lose read ^tfw.

,, 92, „ 7 from bottom, for groce read groote.

„ 132, „ 9, after thai insert o».

„ 169, „ 5 from bottom, for is the only one, read and the

Cambencell church clock, aUo by Mr. Dent, are

the only ones.
" 202, „ 3, after dial insert and one-fifth of the radivs is

large enough,

224, „ 4 from end, for required read requisite,

225, „ 7,ioTj!)eelTesidpeal,
250, „ 5, for it read they.

PREFACE.

I have several times been asked if there was any book on
clock making, which, withont being encumbered with profes-
sional details, would enable a person having a moderate know-
ledge of mechanical principles to understand the construction
of clocks, and the things which chiefly require attention in
their making and management. I believe there is no such
book. Perhaps the articles in some of the Encyclopsedias
might partly answer the purpose; but they are neither
accessible to the great majority of readers, nor do they
contain some information which may be expected in a
rudimentary treatise, though they do contain iuteresting
accounts of some curious inventions, which would be out
of place in a merely practical book such as this professes
to be.

2 PREFACE.

On the subject of chxireh, or turret, or public clocks
especially, there is almost a complete absence of literature.
And yet this is just the branch of the art on which, I am
sure, from what I have seen of such clocks, some general
information is most needed, not only by the public who
have to pay for them, but, I presume to say also, by many
of the clockmakers who undertake to construct them.
Conmion house clocks, like watches, have become merely an
article of commerce ^^an&liheotdy^oBiem is how to make
them to sell. Astronomical clocks or regulators, on the other
6and, are only made by the^hesLmakers, and the attention of
scientific men, both professional clockmakers and others, has
been chiefly directed to their improvement; and when it is
stated that a gbod clock of this Mnd can be depended on
ib one or two seconds in a week, it wiQ be admitted thai
that attention has not been fruitless. But with church and
tuwet clocks the case is quite otherwise. They have been
regarded merely as common clocks on a large arid coarse
scale, and it has therefore been almost taken for granted
that one clockmaker cotdd make them as well as another.
Whereas in fiict their largeness and heaviness is just the
thing that makes them difficult to make well : a chclc, at
least the |ime-keeping part of it, Being the only machine
whone sole business is to overdone its own friction ; and there
is greater room for difference in their construction and
value than in any other kind of clocks.

• Hk' ^antitiwigifc^ which ^wg ;aEe '^ofiMTBied ia esti-
-satui^ iteeObolB of/ aifepemeiili iaiid^ tifieiif (hidaob

•of finlMHi iltfdf is tsdr entkcify 'eiap^;fes!> ^Ml tedly good
idackt «ai ntrar be mBJi^- ^irtlbdttl -s^td^ ^ combination
t<if MmAmiaJfcioal '«imI |fi!M^tk»iI lEk)wledgl^ its of course
isw doAmskeH cam be H^icpk^tdi ' fO ]podses8. I hope
Ad tUs 4f6a(lise ntty tccasiO!!]^ seMcoaUe to

.thMi-ia ilttis res^eot^ aittt 'wfth the ^rieftr of wsikmg It
miro *a r bfcre not schijieS, ^iR^ieHBTter any prac-
tical results -ctep^aidtod on it^ t6 pttt down md;t)ienudicd
results in their most general form^ although in several
faistances the investigations, by which very simple results
are obtained, are too complicated for any attempt even to
Indicate the nature of them in a rudimentary treatise such
as this : I refer especially to the method of calculating the
disturbances of pendulums, given by the present Astaponomer
Boyal-in a paper in the 'Cambridge Philosophical Trausr
actions/ vol. IIL, of which the substance may be seen in
' Pratt's Mechanics/ I may add that it is no detraction
from thje value of those calculations and the formulse obtained
by them, that they aSoati the means of arriving at ^ome
practical conclusions respecting the capabilities and the xaU*
tive merits of the several closes of escapemepats different from
those which were stated by Mr. Airy hnoself, and which
1 have accordingly not thought it necessary to mention.

4 PREFACE.

I have also to express my obligations to two eminent
dockmakers, Mr* Dent and Mr. YuUiamj^ for much prac-
tical information which they have readily communicated to
me for the purpose of rendering this little book more valu*
able, both to professional and general readers. I must add
that it is due to Mr. Denf s enterprise and determination to
find out the best way of doing everything connected witb
his art^ that I am able to state the actual results of
some experiments (of course expensive in the first instance)
which he ventured to try at my suggestion la the two
church clocks I have several times referred to.

From the interest which the subject of the Great Clock
for the new Palace at Westminster excited in both Houses
of ParUament three years ago, as weU as from the many
questions and observations I have since heard about it,
I believe that the short account which I have given of the
proceedings respecting it up to the present time will be
acceptable to many readers. Whether that clock is ever
really to be made is a question which requires some
other science than that of horology to predict. The
government pledged itself to the undertaking by
the commission which it gave to Mr. Barry (at his own
recommendation) six years a^o, as well as by the repeated
assurances of the past and pr^ent Eirst Lords of the Woods
and Forests, that ' all the resources of science were to be

PREFACE. 5

employed upon the Great dock/ But from the time
when. Lord Morpeth gave that answer until now^ nothing
wbatever has been done in the matter. I understand that
there are alwajs torrret clocks exhibited at the French
EqK)sitions; and as this is intended^ we are told^ to be the
best and largest clock in the world, nothing could be a more
appropriate subject for exhibition, and for reward if made
as it ought to be, at the first exposition of manufactures for
the world, than such a clock ; to say nothing of the real
want of it as an accurate public 'regulator,' accessible to
everybody in London, either by sound or sight.

Perhaps I o«glit to apologise for occasionaUy expressing
opinions of my own in a manner which may appear unusual
in treatises of this kind. But several of the subjects I have
had to treat of are so much more matters of opinion as to
the balance of different advantages, than of demonstration
or of fact, that the reader would have had much greater
leason to complain, if I had merely stated just as much as
is ascertained, without giving him any assistance on more
doubtful matters ; and of course I cannot pretend tq think
that, if I am qualified to write a treatise on clock-making at
aU, my opinion on such matters is not worth stating.

I hope especially that the suggestions I have offered for
the assistance of churchwardens and others who want public

CBBfJUCak

olocks^ may (naoaaiottallf kmsskat geGAdoA,iwsb^ ei r^^M
oi)^ to bQ ^rtylaiuad for Ab Inll■ie7^iiiqr have U sp^ifl. If'
the book, elfeete this, or lany ethnr ctf the objeels I ha^iSf
idS^rel to, I dtalt besdlbfied iliat iotjMtn^ (Moml Beif s
isecommondlitiaii io thq pfeiUiBlief^ "bf tbss addiidon tOf the

bftdoes>Lsu8riD0itbeeiLtaiuplfioid«' - . /

i/:.

I • . • . . '.

E. B. D.

' .-. ; '

" ( . "1

42; Queen Anne Street^ London :
1, Jan., X85d.

, »

■ •.• ' 1. ' '. -•'

,;; i iNTK0ti^>U€TrON J

ON THE MEASUftES OT TIME.

, • • • - ' •

■' i. B«Pb!KE ire isxamin^ ^he constraction of instruments
to ^aisttre' tinie, it' "will ^t W veH io niiderstanS cleaffy
whdtlt fs <Rat w6 Trant to lireasmre. • <

'' ^.169. 6l a ceirtaW lei^fli is called a yard, und is ow
stafaiiiM (#ltegtH;''lyttt it ililglri; fast as well have teen
airjr 'otter 'ferigft.' "Thieife 'is'no stch thing as a natural
yard, which we aiti Iqtrite mire'wMieVer we meet with it is
the thing we call a yard, and with which we intend our
sifenllard'- to agife^i "'It Is plirely afbittary, likje a pound or
ai>galk«i.'.^ Aia^t* is^rtOt'eVeij^Wify that if afl

our yard-wands and other measures were burnt, they could
opfj iia re^pr^d bj^th^^j&coi^ ti^ t^^y bose a eertapi.
proportion, (nofy ^etpiPesriUe'^ h Ibng ^(mi^t k^ igoreM, • ta
tK^ lenirfh' of "a periduluni *diat witt vibrate^ certain num-
\^ of. times, ita ai(^j|^aiUi:laiijta4^.0nd:At^a^
ture, during one revolution of ftief earth/ ^ i * • -

8 INTEODUCTION.

This revolution of tlie earth upon its axis is the onlj
natural measure or standard of our time. But it is not
what is commonly called a Day^ which is generally understood
to be the time between two successiye noons or midnights*
But even thia is not the day of twenty-four hours by the
dock^ consisting of so many minutes and-seconds. Let us
see then what a day really is»

2. If you fix a telescope on an axis, so that it can only
move in the north and south plane, and observe the time of
any fixed star passing the middle of the telescope, that is
the meridian of the place, twice ; that time is the exact
period of the earth's actual revolution, without reference
to the sun or any other body, and is what we call a sidereal
dfiLy^ and is always the same ; and this kind of day, with
its subdivisions of sidereal hours and minutes, is used for
many astronomical purposes, and occasionally for correcting
the artificial time shown by ordinary clocks*

3. But if the telescope (which when so mounted i»
called a transit instrument) is directed to the sun, instead.

* This is not strictly true, for sidereal time is really measured
from the transit over the meridian of a certun. imaginary point or
line, which is the intersection of the equator and the ediptic, and is
called the first point of Aries T : and this point has a yeiy slow
preeestum, amounting to 50" in a year ; which, the reader may be
reminded, is a veiy different thing from 50 seconds of time, being iir
fact equivalent to '6\ seconds of time.

SIDEREAL TIME. 9

of a star^ it will be fouad that the sun takes 3m. 56* 5554s.
of sidereal time longer^ on the average^ to pass a second
time than a star does. The reason is that the earth has
been moving in its orbit in the same direction sus it turns
upon its axis^ and therefore^ before the same place on the
earth can i^ain look full at the sun, or have the sun on its
meridian, the earth must tiim rather more than once round.
The time of this passage of the sun is called a iolar day,
and it is evident that in the year there must be one less
sokr day than there are sidereal.

4. I said the solar day was longer than the sidereal by
3m. 56^8. ofi the average. Eor it will be found on accurate
observation that this difference is variable. About the 10th
of February, the 14th of May, the 25th of July, and the
2nd of November, the difference between a solar day and a
sidereal one will be very nearly constant for several days ;
but in the middle of April and June it wiU vary from day
to day about 11 seconds ; and at the beginning of Septem-
ber and at Christmas, as much as 20 and 30 seconds ; and
in February and November these variations have accumu-
lated to so much that the sun appears to be on the above-
mentioned day in February 14 minutefs too slow, and in
November 16 minutes too fast; and about one-third as
much respectively in July and May. This variation in tke
length of the solar day is caused by the elliptical form of
the earth's orbit* However in a treatise on clocks we are

10 INTRODUCTION.

only concerned with the fact, not the explanation of it, for
which astronomical books must be consulted.

5. Since the sidereal day does not suit our ideas of day
and night corresponding to light and darkness, and the
solar day is of variable length, a third kind of artificial and
uniform day has become necessary, now that all the time of
the world is measured by clocks instead of sun-dials. The day
which is so used is that which is always the 3m. 56 '5554s.
of sidereal time longer than a sidereal day; and this
artificial day is called a mean solar day, or more shortly,
a mean day ; and the time shown by clocks is accordingly
called mean time,* And the difference between mean time
jtnd the time shown by a sun-dial or any other solar in-
strument is called the equation of time, which as we have
seen is sometimes as much as fourteen and sixteen
minutes. The equation of time is not quite the same for
the same day, in any two successive years, on account of the
leap-years, but it differs so little that a table to the nearest
second for every day in the year 1850, will be sufficient for
all ordinary purposes, and I have accordingly given a table,
over the next leaf, that it may all appear at one view,
of the time which ought to be shown by the clock when the

* * The astronomical mean day is not reckoned from midniglit, as
tlie common or civil day is, but from the following noon, and has no
' A.M.' Thus 11 A.M. May 1 ' civil reckoning* is, in * astronomical
reckoning,' 23h. April 30.

3HT >ioi :lihat

BaUATlON OF TIME.

.:j< y.

•1 ' // ij o

f. f

6 .'j*,: A V /

sun is on the meridian, which is a very convenient form pf
;Tli§^.table for.pfjffmioatti^, 4si1;i.»fiire8,»Ii;,aftlciil»tioai^ In
I oring the tal^ tpteonine the gqinj; of , a c^odt between any
=^<Miaj£(;bQfote 3all:afl«r a liikrof dE'ebtnAty^yott ninsl tise
jflfe%rrcijttDn giv^n*'i4 theit^Je; for* ^he'^tter Qf 'the two

I i- ' ',

' ^:'-. ^

V. X take £h]^ op^oi^iuiity o|riniii^rtiiig^ short} iaiih of the
ififfcgtenc^ bet^en|©i:e^nwicjlttiine and the local time of a /
jKw Qonsiderable Trapes*: — ' , ; .. ' "

I V

."S 3

1 ■ ■
-^BWninglii^.;;; :.:.(. ^ 7 33'

Chester [] j.l'... ' 11 d&'

E9inbiirgK....»^« >..».. . JL2 4S

:->

i\?-

t ''f <:■

^CimbriclgtJ .•../.

•t

^, xipieter ^.«»r...»^f..».i*i,^... ,. yL4 liJ^;

u^rr.

Colchester
Dover ..'.
, Korwich

*'.

I Boston ,„.,.

' Gksgow ..../.; ,wr..'l7

Hnn ...;.„,..... 1 S

Lteds * 6 -*

■ liverpoQl ......^..... 11 S3

ll£aiichester .».« ». . 9

Newcastle 1 6 34

Oxford ^ «. ^... 5

BftrtamooUi ^. ^... 4 24

Ywk 4 34

SI. James's, Piccadilly ... 33

: ■; . ^

4»l>'

Qtimsby ...;..
Ijputb '...ti..^.

Boris. ..««

Home .........

y^emia .*,....»».

Petersburg ,..
CoiistaiitizM>pk
JTanJuort ...«»«

Berlin

Geneva

■ 28
3 32
' 5 16
5 12

9 21

49 54

65 32

121 1

115 40

53 8^
24 87

TABLE FOR THE

Showing the !nine wbiA. a dock sjioald indicate when the Son

Oajrof
Month

JAllVAmT.

FssmvAmr.

Makck.

Apmxs.

Mat.

Juvi.

H. M. 8.

H. X. 8.

8 51

18 54

12 36

8 59

11 66 57

11 67 26

4 19

14 1

12 24

8 41

56 50

57 84

4 47

14 8

12 12

8 23

56 43

67 44

6 14

14 14

11 58

8 5

56 36

67 64

5 41

14 19

11 45

2 47

56 80

68 4

6 8

14 23

11 81

2 29

56 25

68 14

6 34

14 26

11 16

2 12

56 21

68 26

14 29

11 2

1 55

56 17

68 86

7 25

14 81

10 46

1 38

56 13

68 48

7 50

14 32

10 81

1 22

56 10

8 18

14 82

10 15

1 5

56 8

59 12

8 87

14 32

9 59

56 7

59 24

14 31

9 42

56 5

59 86

^ 9 22

14 29

9 26

.18

56 5

69 49

9 44

14 26

9 9

56 5

1(V

, 10 5

14 23

8 52

11 59 48

56 5

10 25

14 18

8 34

59 34

56 7

10 44

14 13

8 16

59 20

56 8

11 8

14 8

7 59

59 6

56 10

11 21

14 2

7 41

58 53

56 18

1 6

11 38

18 55

7 22

58 40

56 16

1 19

11 54

13 47

7 4

58.28

56 20

1 82

12 10

13 39

6 46

58 16

56 24

1 44

12 25

13 30

6 27

58 4

56 29

1 57

12 39

13 20

6 9

57 53

66 35

2 10

12 52

13 10

5 50

57 '42

56 40

2 22

13 4

12 59

5 31

57 32

66 47

2 85

13.16

.. 12 48

5 13

57 23

66 54

2 47

13 26

4 54

57 14

57 1

2 59

13' 36

4 36

57 6

57 9

3 11

13-45

•

4 17

■

57 17

EQUATION OF TIME:

ii OD the metidum, fot ereiy Day is the Tew 1S60. (Sw j G.)

SLS

JllXT.

A«u«.

9.»>».>.

OnoM..

D«iK>n.

H. M. ■•

H. M. «.

H. K. ■.

H. «. «.

M. K. ■.

H. K. ».

8 28

11 SO 84

11 49 43

11 43 44

n 49 18

8 83

8 67

GS 85

49 24

43 43

49 88

S 40

S 83

SO 18

49 a

48 4S

, *

8 B7

6 48

88 87

48 48

48 44

50 24

4 8

6 42

88 87

48 80

48 46

50 49

4 IS

8 SG

ES 18

48 12

48 48

SI U

4 28

B 80

57 58

47 SB

43 51

51 40

4 88

8 23

67 88

47 88

48 65

82 8

4 47

B 16

S7 17

«7 22

82 88

4 58

8 7

66 57

47 6

44 5

S 4

4 SS

S6 86

48 61

44 12

f3 28

8 12

4 48

56 15

48 88

44 19

83 88

5 SO

4 88

68 64

46 21

44 27

84 24

6 27

4 28

56 88

46 7

44 38

84 63

5 84

4 18

B6 12

45 54

44 48

6S 22

G 40

4 5

54 51

46 41

44 87

H 81

i 45

8 E2

84 80

48 29

45 8

68 20

5 EO

8 40

48 17

45 21

88 SO

B 56

8 26

B3 48

48 6

48 84

67 19

B 6S

53 28

44 65

45 48

57 4Q

6 2

2 58

88 8

44 45

46 2

68 19

2 43

B2 44

44 88

48 18

GS 48

fl 7

2 28

E2 28

44 27

46 S4

69 18

8 a

2 12

82 8

44 20

46 52

59 48

8 10

1 56

El 42

44 IS

47 10

8 10

1 40

61 22

44 6

47 28

6 10

1 23

61 2

44 1

47 48

1 18

8 9

1 8

Btt 42

43 86

48 8

1 47

e 8

50 22

43 52

48 29

2 17

6 8

50 2

43 48

48 51

2 46

14 INTRODUCTION.

6. There is however an easy method of testing the going
<]|f ^ QJopk fcQ3?q^ sid^Te%l^jDil?s»ryi^09|i,,isd^ r^pJ5en(» -j

tjfrfee eqnatioB ^ tiite. -dbij-person of oi Jinai ' j u n d er stand -- -
it^g: wd d^tecitj si^y. ;.cqiisti9ia;fci $ iranpit .itu^npaooiLt^f
sufickttitly cxaJcil for^^thfs purjfosfe^ o^;.^^! a verficil sljb'
or mai^ in % ^^ed iwiA(j!9w^ aod ^the edge. of a -^hjpmejf^ ,
pino^ded id k iipriglit> aiid the 4sJit- lio plicecf as tp te in thfe "
mciidi&n of 4hi^ chi^fie;^ - edge. But :it will nttilrally hp"
aeied how i? the slit to be rb-de; in the jneridian.! Fojr '
ofajmasy astconemy thd fpiUowing methoid wiU be jsufficientlr '
apcnrate. Kx iipon'a vtrtioai'edge 4f'a cTiinmqr dn the '
sotlth ef sotiae *iHndpw^. ^^Detei*Biiie fiifet^of all,! by seeing ^
wh^&the shadow of the.3Tin {^Ila>^t ^(^aioon^^or^herei-
abokit*) which pane ^rfll fce theproper one fbr the- |)ittpos^, ' '
and* get the dock set as tiearly as you can to thelright tim^, '
eilSierby tradiden from idme persbii who jpdssessiBS^thjs traje
tii»ie, or from an accvqrata sun. di^ Bod in anj^Jipianak;
which gives «uck thiiigs ^ftie tinie trf soufMififf, or pasang of '
tjie meridian, of any ^bwn star or planet which happens to he
visible at a coiivenient time fallowing for your longitude,
if any> from Crreeprcicii). Whai the ^ dock is near the
tjnie at which tiie star-ought to be on t^e jneridian, stanjd'
by the window with a sheet ot tin made exactly rectangulair
Ki^ capable of sliding al^g iihe pane, re(rtiQg on the bar of.
the window (s«5)popiiig it to *e horixontal). When the
<3lock is exactly at the time of southing of the star, yoa
must place the tin so thai you just see the planet past the

CHEAP TRANSIT INSTRUMENT. 15

edge of the chimney and of the tin ; and there the tin mnst
be fixed, or the glass marked and painted up to the
mark.

If the edge of the chimney was its western edge, the
planet will emerge from behind the chimney ; and then, if
the glass is painted on the western side of the vertical mark,
by putting your eye nearly in a line with the mark and the
chimney edge, you can enclose as fine a line of light as you
please between the edge of the paint on the west side of the
meridian and the body of the chinmey on east side, or vice
versd; and that fine line of light is the line which stars have
to pass when they pass the meridian. Before the mark
is finally fixed, the operation ought to be performed several
times, as there is sure to be some loss of time at the first
trial in getting the tin to the proper place. You must
observe the time of transit by listening to the number of
seconds from the time when you looked at the clock.

Now when you have got this meridian line, even if it is
not perfectly exact it will do very well to try the rate of the
clock by, though not to tell the absolute sidereal time,
unless it is either quite exact or you can learn how much it
is wrong. To try the rate of the clock, observe the time of
any well known star passing your meridian; and go and
observe it again at the end of one or more sidereal days.
Your clock ought to be behind its former time, at the

16 INTRODUCTION.

rate of 3m. 55*9093s. of mean time for every sidereal day
between the two observations.

7. Still we want to know how to ascertain the actual
mean time from a sidereal observation. Now or 24
o'clock by the sidereal clock of any place is^ as was stated
in the note to p. 8, the time of the imaginary point r
passing the meridian of that place. And from this point
the right (ucefmon^ or distance along the equator (corres-
ponding to terrestrial longitude) of all celestial bodies is
measured; and it is generally expressed in almanacs in
sidereal hours and minutes. Therefore in fact the B. A.
of any star^ given in the almanac^ is the sidereal time at
which it passes our meridian, since r was on the meridian
when the sidereal time was 0. But the mean time was
when the mean sun was on the meridian; therefore the
E. A. of the mean sun substracted from the E. A. of the
star (with twenty-four hours added if necessary) is the
number of sidereal hours, &c. that have elapsed from mean
noon to the time of transit of the star ; and this number
of sidereal hours, &c. may be converted iuto mean ones by
multiplying them by '99727, the ratio of a sidereal to a
mean day; or if you substract 9*83 seconds from every
sidereal hour and 1 second from every 6*1 minutes, it will
give you the time which ought to be shown by the mean
clock at the transit of the star. In some almanacs* the E. A.

* One that rejoices in the singular name of Zadkiel's Ephemeris

CHEAP SUN-DIAL. 17

of the mean sun at noon is given for every day under the
head of sidereal time merely. If the B. A. of the real sun
only is given, that of the mean sun is found by merely sub-
tracting the equation of time when the clock is behind the
son, and adding it when the dock is before the sun.

8. The more obvious way however of finding the error
of a clock is to observe the time when the Sun passes the
meridian ; and if the time then shown by the clock does not
correspond with the equation of time, the clock is so much
vrong. The sun is too large to be observed directly like a
star at the moment of passing ; but it may be observed by
the same method as I have described for a star^ if the times
of its western edge first appearing and the other edge dis-
appearing be observed (with the help of smoked or coloured
glass, or a fog), and the bisection of them taken for the
time of noon. Various kinds of meridian sun dials may be
used, and no others can be very accurate on account of the
refraction, nor can they be so easily made. If a narrow
vertical slit is made in any thin plate &cing pretty nearly
south, the bright line that comes through it from the sun
will always fall in the same place at noon on any surface
which is level in the east and west direction, and it can be

gives it, for the special purpose of saving its constilters the trouble of
adding or subtracting the equation of time. It may of course be U3ed
for horological purposes without the necessity of believing in the
more abstruse science for the benefit of which it is published.

If) imaQPVotioQE.;

deasribo bor-ftiAeiifliaiiriiibik.oE iUi Und nn^ b&niide'
wtAeat toy. eahknaossAsn^anee;. ' < . ,- - '■ i '.'•' ■

Make ■ Hmall Imle da a thm' fi»i» of'pMated'tai.'Or I
brasSj set facing the south in a window-frame or other I
fltmmBfl&t piaee.. Flare a P^bss «f -ikte or b smooth board
4|Kt« knfil i^dnsi the< jdbto, Ukd Abeot 9 inches bdow Mtb
bole. I 9B5qnitel^(^^iecatH»ituea«flrionnk£FitleV«l
in Hi«[7 ^recticm thiiL,t»'£lid -out io-t^ -flitt iat^i^oe vMtft'
it the eastand west direction. Sot after the meridian it
fitrtmd, the bond nay^bfl sloped i^loimi^ the semth, sat
tikCAhadoiTTiUbs idcaiat^'-aad ehsipei tbra if M is' }evd^.
Morenrrai, tlubnght^^denrof ithe htde-ii^ b«''cl«u«t< S
fhe plats is butw is tote puiUcl totiwen^fj asis;>1f
itinakes an u^ of »b4al 4&? with'tbe^verticallt WiQ-^
fnita i the'tole'iii 'tlie
' plate drop 'a perpeiidi-
feular A ij upon "t'he
board^ and'iiMe a mart
at C. it a little after
11 o'iJIock on a feie
day, observe where the
image of the Sun falls
on the board, and mark
the pla^^e of ita ceotre.
Su and dnw & iftrele on the betfd with tafias &«,.

Qbsenre'the pbee of ike bii^vpetvii imo ddnei times before^
noon^.and yuA. {faemJft,, 83^ and dnnr circles far IkcOft m
lakamaaiifirw ThoD^if thelaiikcbservsttaiiirBBittllb. 46^
go agam a> little before 1^&« Mm., and \99^teb lov tbe pas**
81^ of tiie 9po4 over r^be ftf«l ^iireH and make the ^aoe^
vbere the enatre eioates^ ft^ 0^^ and do tbe «M» with tii»
other circles. Bidi^t 1^ thi^^ >atei» Si 8x> % s^t, C^ Sjj mxt-
if you can draw a straight hne through all the bisections
aad tbe. goint C^ ^t &ie B C is tte in^ffim Jine on
whibh tine image Bf i^e sita wiffi ^ajis ft!Q at solar noon/
«ad the padeiig^ fi ihe )spbi& can be dbsened rtexAf to a
aetecmd. T!d» lAerdbre n4tli 4he equattE>n4»ble wifl giver
the meaiw of ^tteetifig a doek on any feie' day. . Befttf^
<he Ene is strongly uiarKed it vfM be as w^ll to try it both
iii flntmmcfr ted at the disfcfaee ot thiree' or fottr months.
This apparatus is so fcfcsily made, and so nseful irien it is
made, that eveiy dockmaker who has not the means of
dbtanring the thrie from an observatory 6ng!it to hare one,
for it is no nse having clocki? tiiiless you ean contmually
recnr to wliat maybe called the daium line, from which they
are to measure, viz., mean noon. Ihere are many large
towns in which there are literally no means of recovering
ffic tnte time whek it i lost except by sending somewhere
else to f^tch ft; £hid th^re arcj very fefw people who are able'
to take it- aGturatd!y when they ^Q^\t, " -"■''•

* %, 5Chereis besides IKig simple kind of meridian dial,*

20 INTRODUCTIOK.

which anybody can make^ a very beautiM little instrament
invmited a few years ago by J. M« Bloxam, Esq.^ of
Lincoln's Inn^ called the dipleidascope, from which^ laien U
u once accurately fixed, the time of solar noon can be
observed with even greater accuracy^ on account of the
increased sharpness of the images which it produces^ as well
as their passing with considerable velocity.

It presents Wo bright images of the sun, which
approach each other, and exactly coincide at noon; and
thus two observations of noon are obtained, viz., the time
of first contact and of final separation, the bisection of
which gives the time of noon, and the time of complete co-
incidence. It is of no use to describe the construction of
the instrument, as few persons could make it, even if they
could legally do so ; Mr. Bloxam has transferred the patent
to Mr. Dent, who makes them, and from whom also Mr«
Bloxam's pamphlet on the principles and construction of
the dipleidoscope may be had, as well z& the annual equa-
tion table, which is for this year that given a few pages
back, to the nearest second.

10. I have no intention of inquiring into the history
of the various instruments that have been used for horo-
logical purposes; Sun-dials, at least for noon, could not
fail to be very early used, from the obvious fact that the
shadow of any vertical body always Calls in the same place at

WATEB-CLOCKS. 81

the time when the length of the shadow was least in every
Jay; and it would be easily observed that the intervals were
very nearly eqnal. The sun-dial of Ahaz will occur to
every one. But probably much more accurate astronomical
observations than any that can be made with a sun-dial
liad been made long before that time by the Chaldeans^ for
without accurate measures of time astronomical observations
can hardly be supposed to exist*

11, Everybody has heard of the clepsydras^ or water-
clocks of the ancients. If a vessel of water is kept fiill by
. ^^ runniBg through it, and a Me is xnade near tl^
bottom^ the water will run out of the hole and fill any
other vessel at an nnifonn rate; and this other vessel may
have its sides graduated, or carry a floating index pointing
at a graduated plate divided into hours^ and even minutes^
if the index rises fast enough to distinguish them. When
the index gets to the top it might be contrived so as to
open a valve and let the water out^ and itself go to the
bottom again and shut the valve ; and if this was made
to take place every twelve hours it would make a self-
acting clocks requiring no assistance except &om the stream;
If, on the other hand, a given vessel is filled and gradu-
ated according to the rate at which the water flows out,
which is not uniform, but varies as the square root of the
lieight above the hole at which it stands, this also will
serve for a clock until the vessel is empty:

^e anovoamm.

12; fiand rammg out of 4k. iibfo a^ Hbe b6tMih
^. a Toad >k)Wfe]* notf irii& vtftry ^etuiy Ittiifti^rtti
Tebcky; fofr oik' aaxmA ^ 'At fri^tiktt be^o^/flfe
pwiJckflTi wUMl does- not exiiaA^ » a: Adid, the MuS
only ialls out, «ad' is nol {Misdpl d8it> bf VzrtiJM! of
tlie flame pnnfl9pi& wUeh e&able» «t^d to-n^ uf ft ^be^
blasrtaitg ]iole^ JEdiiae.it» Anautrt^ctf ^p^nsofe <^«in pisli i
considerable thickness of. MOid ilanyogli ft tab^ ^itbotrt
burstmgit. I have seen no account of an index fixed to
•im bdinvglMd^ that is to a s^nd-gkssr; Ircct <m6 might be
Blade dQ fiie plaen c^ those tojv in* ifhich isand runs into
a smafl budiat^ which tiEms ever when it is ftfll^ moving
BOBie figoiie df ft Mm ^ aninud wi1%.' ft. Hds might be
made ta t&lsef jfece e^ eirery imnttte or other intervial^ and
might issm^ tr dock-hani accordingly. Since 1;he invention
^clodsB idefMsydras have been madd as trtiriosHies^ probably
much mows perfect <^n any that existed before. Bat these
things now bel(mg lathei! to the department erf * philosophy
in sfort/ tihtan ^ sdence in earnest/ and a description of
•Saaok woold be oat of place in a practical treatise on clock-
making.

.'" -i.'-'l f \:;

f . . « * T <

'\ ' ' r J .••■ - ■', • ' •..■•••.■ . .•.-.'. ',

•

-ON ...

'.■■''.'.• -' ' .' ■ ' • • ■ '

. eLGGK A#D WATCH MAKING.

j ".:'■■% ; •'• ' ■ ' ' . ■ ■'• ' •

. • i ..»••, t"*^' ^ « ^ <t tii >^ i t *t»i i j i> 4« n -^ "^ly* ■■^i"-

i. •■••.'•■ . -

. ...-,. ... .'CHAjrrwJ-.
- ' ON CLOCKS.

ISr A <3l^ck baa i^ometitnoa Inte dfefineft to Le a 2Ki£k
.0luiie£ot.€0m#f^ibe vlbtatimts of apcndnhun^ aiid soitie ;
l^ut thk.ia hikr^y.a veoHTeet dbfimticm ^ for il iu^Iies fostly^
that tbeclopk faiuijaaihii^todDbirt toooiuittihe vibrstiond^
wbeoa^ ii baa akK) to Biaiataiii them, a^. & pendolum witt
iioi gD 0B:l(mg endnging bj iteelf ; istca&dlj} tbat the «lodi^
fices not alter.tbe tiBieofTibratiQii: ^vrhkb it does* find tliiidly^
thattpen^yteiaflr aDii» o*he» vib«tmg bodjrw essential
toa elock : 'which il is not ; forolocksne aetudljn^ide on
the pciiaoipii^ cf hismi^ the velocity of ihieir moinement^
detenaiaed by a. revolving fly, either with fans to which the
air offers a Kcsistiaioe^ m wiih a heavy xim^ whose own
mametU <f inertia prevents it from moving tiw rapidly*
A more cotreot defiiutian would b^ that a doek or a watcH
is a machine, ^(maktiiig of a trakt of wheeb turned by a
vvvighty a fspmigy or any other nearly resistant fisrce^ and ti

24 CLOCKS.

which the velocity is regulated bj attaching to it a pen-
dnluin^ balance^ or fly wheel, which always vibrates or re-
volves nearly in the same time. And the only distinction
(except the arbitrary one of mere size) between a clock and
a watch is, that a watch will go in any position, bnt a dock
only in one.

14, The invention of clocks with wheels is ascribed to
Pacificns, Archdeacon of Terona, in the ninth century.
Clocks (without water) are said to have been set up in
churches towards the end of the twelfth century; and there
is a story of a clock being erected in Westminster Hall
in 1298, out of a fine levied on a lord chief justice ; and
near the same time a dock is said to have been put up
in Canterbury Cathedral, and one in Wells Cathedral in
1825. Mention is also made of a clock, apparently of
some new construction, invented by Bobert Wallingford,
Abbot of St. Albans in 1326, and which was going in
Henry the Vlllth's time. Prom these and other notices it
seems pretty clear, that, though the earliest clock of which
the actual construction happens to have been preserved, was
that made by Henry de Wick for Charles the Vth, in 1379,
yet he is not to be looked upon as the inventor of them.
According to the description given of that clock, it differed
in nothing, except in having a horizontal balance iostead of
a pendulum, from many old church clocks still in existence,
being merely a thirty hour dock with one hand; and the
striking part was exactly the same as is still used : in fact
in some respects it exhibited a more advanced state of me-
chanical art than the clock (I do not know of what date) not
only in existence, but in action, in Peterborough Cathedral ;

ANCIENT CLOCKS, 25

wMch has a wooden frame instead of an iron one^ and
instead of being wound up by a key or winch, is wound up
by long handles or spikes stuck into the barrels. It has
bowever a pendulum. The going part of the clock has
indeed lately been superseded by a modem one; which
is far less creditable to the mechanical skill of the time at
which it was made than the old one, especially consideriag
that it has no dial to work, a circumstance which affords
unusual faciUties for a good clock. The old striking part
still does the striking on a beU of considerable size,

15. !From these old church clocks have descended all
the modem race of smaller clocks and watches, which have
arrived at a degree of perfection which seems truly won-
derfol, when it is considered that, though there is no
such thing in nature as a perfectly isochronous pendulum
(one which vibrates different arcs in the same time), and no
such thing as a train of wheels with perfectly uniform action,
yet penduluias can be kept vibrating with no greater devia*.
tion from isochronism than one beat in half a million. In
the mean time the church clocks themselves have descended,
. in the hands of all but a few makers, into little better than
ironmongery : and many of them display the grossest ig-
norance, not only of horological, but of the commonest
mechanical principles. Perhaps the most striking instance
of neglect of horological principles is the practice, of whidi
Mr. Vulliamy in his ' Considerations on Public Clocks'
gives several rastances, of putting fans or wings to the
pendulum; I sappose, for the purpose of preventing it
from occasionally swinging so far as to drive the pallets
into the scape wheel under the iofluence of such a weight

26 CLOCKS,

as was found necessary to cany tbe tram through all the
occasional impediments arising from bad cutting of the
wheels^ dirt^ the force of the wind upon the hands, and all
kinds of mechanical defects. It is remarkable that, until
lately, the French have been much in advance of us in this
largest kind of horological engineering, and have spent
much larger sums upon their public clocks. Mr. Yulliamy
mentions no less than four in Paris, which appear each to
have cost about £1000, .exclusive of* some other expensive
appendages, such as enamelled diab, and the bells. There
is not a clock in England which has cost anything near
that sum, exclusive of chimes and other appendages, which
do not strictly belong to the clock. The estimates for the
Great Clock for the Jfew Palace at Westminster indeed
exceed that amount; but that is to be a perfectly unique
specimen, combining unusual size and unusual provisions
to secure accuracy of 'performance,' as the clock making
phrase is.

Of late, however, an improved style of turret-ckx^
making has been introduced by some of the best makers.
And since the erection of the clock at the Boyal Exchange,
which contains several contrivanees never before used, there
can be no doubt that, if we choose to pay toi it — and leaa
than half the cost of the above-mentioned French clocks
is sufficient for all but the largest clocluH-we can have large
elocks made just as well as small ones. The present as-
tronomer royal (who certainly cannot be accused of undue
partiality to his own countrymen in matters of science) has
said that he has no doubt that the Exchai^ dock is 'the
best public dock- in the world/ and thrt he f believes it is

REVOLVING PBKDULUM. £7

BapericMT to most ftakonomioal clods in tlie steadiness of its
tate.'^ Of course this degree of accuracy cannot be ex«>
]pected in imy but &e v^ best docks; but by merely
attim&ig to a hw simple considerations they may certainly
he ioade, and irithoBt any great addition to their cost^ to
•pproooh to the accuracy of all but tiie most highly finished
astronomical docks or Tegulators, instead of being, as thef
frequently are^ merely the public exponents of the time of the
best clock which the man who 'looks afl;er them^ happens
to possess, or of the nearest railway station clock, which is
probably a small spring-clock tiiat cost £6, and is set
right when it gets as much as five minutes wrong. .

16. It is evident that a fly, either witii fans or weights,
would, if the resistance of the air and the friction of the
maohinery w^ie uniform, produce a constant velocity in a
train of wheels turned by a weight hanging by a string
unwound from the axis of the first wheel in the train. One
would imagiBe therefore that tiiis would be the earliest form
of a dock, as it is the most simple, and a fan-fly was
actualfy used in De Wick's dock, as it still is, to regulate
the ¥ek>cily of the sinking part. Whether this was so or
not, we haw no meansof knowing; but it is worth noticing
ihat that oonstnidion, or a slight modification of it, is
actually in toe now. The dock which is nsed to keep the
great «qaatoreal tdescope at Cambridge in motion opposite
to the motionof the earth, so that it may remain for some
time pointed to a given dtar, and not move by jumps as it
would if dm«n by a dock with a vibpitmg pendulum or

# * '

* Parliamentary Papers respecting the Great Clock for the New
Paiaee.

68 CLOCKS.

balance^ is r^ulated by a governor j like that of a steam
engine; which is also called a conical pendulum^ because
the rod of each ball describes a cone as it revolves. As
the force of the train increases the velocity of the balls
they fly farther out^ which increases their moment of
inertia or resistance to motion^ and may also be made to
apply an increasing Motion by means of a spring to some
part of the clock, and so restrain the increasing velodtyi
as the governor of a steam engine regulates the supply of
steam to the cylinder. Such pendulums have not yet been
made to approach the accuracy of a vibrating pendulum
with an escapement, being much more affected by any
variation in the force of the clock. The time of one
revolution of such a pendulum in a circle (which it cannot
always be persuaded to describe) is the same as that of a
double oscillation of a vibrating pendulum whose length is
equal to the height of the point of suspension of the
revolving pendulum above the plane of the circle in which
the ball revolves; which will of course vary as the force
that drives the pendulum varies. There are other practical
difficulties in their use; ajid it ai^>ears to me that uniform
continuous motion of a train that has heavy and therefore
variable work to do is more likely to be obtained by the
method which I shall describe under the head of train
remontoi/ren (176), than by any contrivance for reguUting
the motion of a conical pendtilum by friction.

17. Most people know that a clock consists of a train
ef wheels, generally four, of which the lowest, if it is an
eight day dock, turns round in about twelve hours, or
requires fourteen turns to wind it up for the w^, m3i the

CLOCK TBAIN.

tt^hest tnnia in a mmate. l%e two intermediate wheeU
ate msteij required to cany off the difference of velocity
between the two extreme ones and to work the hands.
Tbe lower of ^ese two intermediate wheds is osnally mad*
to turn once in a hoar, so that the long or minnte hand
may be set ajxin its am or arbor produced as far as the
face of the clock ; and the second wheel has nothiag to do
hut to reduce the multiplier of Biity, or the ratio of the
velocity of the highest to that of the entire wieel, as the
one which carries the long hand is usually caUed. It may
he convenient to give a sketch of the common arrangement
of the going part of a dock, with the different parts marked,
boia which their action will be pretty evident.

18. The string is coiled
aixteffli times round the
barrel when the dock is
wound up. The barrd asis
or arbor has s sqnare end
to fit the winding k^, and
when yon turn it to the
right the iat«hett teethe of
which three or four are
shown in tJie drawing, raise
the dick which is fixed to
the great whed and kept
pressing gainst the latch-
ett by a spring; but when
yon stop winding, theratch*
ett teeth cannot pass the
other way, and so the weight acts upon the whed, tending

19 cxioccs.

t6 Htmnf it'to the left ' The.^ieat wheel has imOSlf
^inel^Hrix tKA> andfitt dbdvee tbeditile wh^ (>r jpifiidii
of jldul QBtttrft wlKe^ lAkhi hae cigbi teeth ^* kim^ aM
ilMnfq^e goe^: Wneltt tinies as ftat.as^ 1^. ^revt wl^*
inbftfqmtrfa^vHka^ chlvirfttliti {liw^feuel: ti^ej seaond wfa^
frliA iAv«a fto mipf iriM^^mA '%mk teetk an^ \smm

ofieltTOSi oil tte saap^ wliael pinion^ jK^of fli& aecSond^wh^
pfiliasiy^kiid i^' ited) i^^ iiid ntaoibaar/of the to^tli thai dma

tiiem respectively, — ^ — ^aay = ffO, The only conditions to

lie obeereed are, that no driven pbdon onght to have kaa
than seven leaves at the lowest (except of a land whidi I
ahaH mention hereafter) ; and that if the teeth of both
iseheeb are of the same size,, the centre wheel nmst \m^
more than, or at least as many as the aeeond, or they
couldnotbegotinto the frame togeflvar. Suppo-e eitfw
jpj or jt?, to have seven leaves aind. tiie othar:eigl|t^. the^l
i^ t^ mnst = 60 X 56; and those twj> ntambera 6Q i»id'5Q
inU do for the teeth of those twb. \idiedls #s.W9ll a3 any
jt)ther numbers giving the same pto^^ct. . . %

19. With regard to the weight, the t&s^t <will ob^csrvf
that it hangs by a double line, or' a siDgle moveabid piiillej^
the effect of which is that only half the weight realfy acta
iipon the clock; but then the string is ilpon the whafo
flouble the length of the actual- fall (tf the wei^t, aM
therefore the effect of the weight is jog^. the -same if it Wera
hun^ by one string and had the same fSedl; in which caao
the barrel would of course have to be only half the size, or,
the. number of teeth in the wheel doubled, or the nurnb^

CLOCK TRAIN, PULLEYS. 31

of lea?es in the centre wheel piiiiim ' haired. Li com-
padiflons of clocks one aometmies sees calculations of what
the weight is eqniyalenbto 'on the single Une/ or what
IB worse^ a mere statement of the weight withont any in*
Satmation as to its taH, which is jnst as necessaiy an
ingredient in the comparison. It does not signify (oLcept
as regards the friction of the pulleys, which cannot be re^
dnoed to calcaktion) what the weight on the single line is,
^r whethip there is one line or a dozen : a given weight
fidKnga'gi*«n Knight is equivalent to itaelf, andtonothing
^se, except anothv wioghb falling a height as much greater
« less as flifi weight is lessor greater. Therefore in every
possible .case if jon want to see how much of the ' first
power' of the dock is wasted in the Motion of the train
andpuDfiy^ or.howmTidi.a;givmycap«nBBtreqniieg, you
have nothing to do but^ to \ remove the .pallets and fix to
the scape wheel or its arbor an arm of any lensth that is
conv Jent, and hang small weights to the end of it, till
y<m finid what w^ht the dock will just deddedly'lift,
Hm atm being horizontal. The arm should have a cpun«
terpoise and be as light as possible^ so that its own weight
may not enter into the question or add much to the Mdion
of the iSttape whed pivots. Now if you know the fall of
the <doak. weight for eight days, you know it for one day,
and one minute, or one revolution of the scape whed,
whatever it may be, or any aliquot part of that revolution;
and if you know the length of your measuring rod you
know that its end would move through a space 6*28
times the length of the rod in one revolution : or, without
that calculation, you may turn the scape wheel through

32 CLOCKS.

^ne-eigHth or one-tentli of a revolution, and measure liov
much the little weight rises therein. Sappose this rise is
6, and the corresponding fall of the great weight a;
then the great weight w ought to be to the little weight m
as b: a* It will in fact always be a great deal more, and
the amount of the excess oiwa over mbin different clocks
shows the comparative loss of power in their trains.

20. And again for the converse of the experiment aa
regards the escapement (of which I shall treat presently)
when you know what the momentum of the clock weight
really amounts to by the time it reaches the scape wheels
you know how much of it is consmned in driving the
train, and how much goes to drive the pendulum. These
proportions will be found very different in different clocks.
But it is time we should proceed to exphiin what that im.
portant part of a clock called the escapement is.

ESCAPEMENT.

21. An Escapement is a contrivance by which the
teeth of a wheel, commonly called the scape wheel, are
successively let go and stopped at certain short intervals of
time. In all the common kinds of escapements there are
two pieces of steel called pallets fixed to an axis which
vibrates, so that as one pallet moves out of the way of the
teeth, the other moves into the space between some two
teeth, and so stops j;he wheeL Consequently as every tooth
has, at some point in the revolution of the wheel to dear
both pallets, there will always be twice as many beats in one
revolution aa there are teeth ia the wheel. But the es-
capement must do something else : the pallets must be of

ISCAPBUXNT. 33

flach a sliape that as the teeth escape tliey shall give a posh
to the pallets, and this posh is commaiiicated to the vi-
brating axis, and to the peiiduliuu or balance, which is
attached to it. A baltmce is simply a &y wheel, and was
no doubt first called a bahmce, because in the earliest clocks
it was in the form of a balance and not of a wheel, con-
sisting of two arms set npon a vertical a^ and canjdng
weights hiiog at the ends of the arms. This was the form
(rf 1i,e balance of De Wick's chick : aS^^wards the weights,
instead of being hung on to the arms, were screwed on, so
that their distance from the axis could be adjnsted more
accurately. The escapement was. exactly the same as that of
a bottle- jack, or the commonest kind of watch, and is called
a verHcai escapement. The pallets are two flat pieces of

34 CLOCKS.

f^j&Ap,p, set on to a vertical axis^ in planes aboat at rij^
angles to each^other. In this drawing the highest tooth (rf
the wheel (which is from its shape called a crown wheel)
fe represented as just escaping and coming forward (or
towards the reader) ; the lowest tooth then strikes against
the lower pallet^ which stops it; and not only stc^ it^
but, as the vibtation of the balance in that direction cannot
be suddenly stopped, the pallet advances a little further
forwards, and so brings the wheel back a little, and produces
what is called the recoil, which is, in a less degree, com-
municated to the rest of the wheels, and ultimately to the
weight which drives them. It is evident that each tootii
as it escapes gives a push or impulse to the pallet wUicb
presents a sloping face to the direction of the tooth; and
so the time of a vibration in this clock d^iended upon the
force of the impulse relatively to the moment of inertia of
the wheel, except that a greater force would catise it to
make larger vibrations. The effect of such an- escape-
ment as this may be judged of by taking the penonlum off
a common clock, leaving the cratch on, and observing the
difference between the time the hands will take to make a
revolution when the weight is in its original state and
when it is added to. In a bottle jack the piece of meat
and the iron wheel which is generally hung to the jack
together form the balance. The jack is driven by a spring
instead of a weight, and the velocity of rotation of iihe joint
diminishes as the [Spring runs dpwn. The ^cape wheel of
the vertical escapement must either, have an odd number
of teeth, or the axis of the pjJlets m^st be a little on one
side of the centre of the wheel.

PENDULUM. 36

PENDULUM.

22. Clockft remained with balances it seems for about
300 years after De Wick's time; And there was a great
dispute as to the first inventor of clock pendulums. It is
usually stated that the fEumous Galileo discovered (as he
3uppo8ed) £rom observing the swinging of a lamp hung
firom the top of a churchy that pendulums oscillate
through different arcs in the same time: a property
which is called the isochrpnism of , the pendulum. It
is said, however, in the able and 'interesting artidd on
clocks in the Ewsj/clopadia Britannic^, (last edition), that
this cannot be reckoned among the ^S|fH)veries of GaU*
leo, ' for the andent astronomers of the East employed pen-*
dulums in measuring the times of their observations,
patiently counting their vibrations during the phases of an
eclipse or the transit of the stars, and renewing them by a
little ^lih with the finger when they languished : and Gas-
sendi, BicdoU, and others in more rec^t times followed
their example.'

It is iLot indeed strictly true that pendulums do vibrate
different arcs in the same time ; but it is true, that so long
as the arcs do not exceed a few degrees, the oscillations ar&
very neady isochronous. And, therefore, if a pendulum can
be kept twinging nearly the same small arc, its oscillations
will be so nearly isochronous, that the difference will
not be sensible except in a considerable time. This dis-
covery would naturally lead to the application of the pendu-
lum to docks : and as is usual in such cases, the invention
was probably made independentiy by several persons about

CLOCKS.

the same tinier And in favour of the daim of Harris^ the
clockmaker^ who is said to have made a pendulum clock for
St. FauFs^ Covent Garden^ in 1621^ several years before
Dr. Hooke^ Huygens^ or GraUleo's son^ who all claimed the
inve^tion^ it may be remarked^ that if, either by accident or
design, he placed a clock with the axis of the balance hori-
zontal instead of vertical, and left one of the arms without
its weight, he wonld see that he had made a clock with a
pendulum, of which the isochronism was probably by that
time generally known, and he would naturally adopt it
immediately.

23. But whoever was the inventor of pendulum clocks^
there is no doubt that Huygens was the discoverer of the
true theory of the pendulum ; and though his application of
the theory to practice is now abandoned, yet as aU pendu-
lum calculations depend upon it, it is proper to give a short
explanation of it. He discovemed that the curve in which a
body must move so as to oscillate large and small arcs in
the same time is not a circle but a cycloid; which is

the curve genera-
ted by a point P
in the circumfe-^
rence of a circle
D E P rolling on
® a straight lineB CL
And he also found
that it has this re-
markable proper-
ty : that if the cy-
cloid B P P C ia

CTCLOIDAL PENDULUM. 87

cat in two at its lowest point "E, and the two halves put
together as in this figure^ CF being placed in the position
^'B, and BF in the position AC^ then the end of a string
A P of the same length as AB will^ as it unwinds firom A B
and winds on to A G^ redescribe the original cycloid B P F C^
This is expressed mathematicall j by saying that both the in»
volute and the evolnte of a cycloid is an equal cycloid. Con*
sequently if a weight or bob were hung on to the end of the
string AP^ it would be a pendulum swinging between the
cycloidal cAeeis A B, A C, and describing the cycloid B P F G;
and such a pendulum would make large and small osciUa*
tions in the same time^ or would be perfectly isochronous.
Nevertheless it is found that the impossibility of making the
cheeks so accurately as to cause the pendulum to vibrate in
a true cycloid^ as well as other causes, all apparently insigni-
ficant, so much disturbs the isochronism of such a pendulum^
that it is more isochronous, even up to arcs of 6*^ or 7^, with-
out the cycloidal cheeks than with them.

24. It will now be evident why pendulums swinging in a
circle in small arcs are nearly isochronous, and more so the
smaller the arcs are; for if you describe a circle with the
radius AF, it will very nearly coincide with the cycloid for
a short distance near F, the lowest point of the cycloid, but
will deviate farther from it the farther you go from. F ; but
the smallest arc in the circle really takes more time to
oscillate than the largest in the cycloid. The difference
between the time of any small arc of the circle and that
of any arc of the cycloid varies' nearly as the square of the
circular arc, or of the angle which it represents; and again
the difference between the times of any two small and nearly

88 CLOcfcs.

equal circular arcs vanes as the arc itself; tliat is^ if a cloek
pendultim is swinging 4^ from zero^ and from some cause
the arc is diminished 5' or 10'^ tlie clock will gain twice as
mucli as if it liad only been swinging 2^ when the same
diminution took place : which is just the opposite of what
would probably have been guessed. This is called the
circular error, and if a is the arc, and da the decrease of it,
the gain of the clock in the day (supposing it to have a
seconds pendulum) is 10800 ada sss rather more than 1
second, if- « = 2° or 'OSS (the radius being unity) and
da 3= 10'.

26. It is well known that a two seconds pendulum is
four times as long as a one second pendulum : that is to
say, the time of vibration of a pendulum varies as the
^square root of its length. But this does not teOi us what
the actual length of a seconds pendulum must be. Let
; be this length, and t the time of one oscillation measured
in seconds ; ir the ratio of the circumference of a circle
to its diameter, or 8 '1416 ; ff the force of gravity, which
is expressed by the number of feet per second, or the
velocity with which a body is falling at the end of one
second, or twice the height that it faUs in a second ; then

^stty/— . Ill England ^=32*2 feet; and therefore the
length of a simple pendulum to vibrate in one second of
mean time must be 39* 14 inches nearly. And in like
manner the pendulum to vibrate sidereal seconds must be
39'14x997*=38-87 inches (§7). I may mention here
that a clock with a pendulum for mean time may be made
to show sidereal time (though it will not mark sidereal
seconds) on another dial, by the ^addition of four wheels

PENDULUM. 89

and two iarbors as follows. Put a wheel oi 247 teeth ou
the centre-wheel arboi" of the clock, and let it drire a«
wheel of S31 teeth on an arbor which also catries a whedk
of 48 ; and if that drives one of 32, this .last wheel
willserve for the ceatre wheel to carry the nanate hand
of the sidereal dial; .as it will torn slower than the othep
oentrewwheel in the ratio of sidereal to mean time within
a fraction of no more than -nmr of a second in a day."^

I spoke jnst now of a eimple pendntum. A simple
^ndnhm is, what can only exist in theory, viz., one
in whieh the rod has no weight and the bob consists
only of a singly heavy point. The weight of this point
or oob is of no consequence in the theory of the simple
pendulum, though it is, as we shall see, of great con-
sequence in practice in resisting the various disturbances
to which a pendulumi is subject. Every real pendulum
however (which in mathematics is called a compound pen*
dulum) is equivalent to some imaginary simple pendulum;
and the^thirmer the rod is, and the heavier the bob, the
more nearly the real pendulum will approach in length to
a sunple one of the same length, measured from the point
of suspension to the centre of the bob. When the rod
and th6 bob'are of any regular shape, as they generally are
in clocks, it is not very difficult to find by calculation the
length of the equivalent simple pendulum, or the distance
from the axis of suspension to a point in the real pen*
dulum which would be the bob of the simple pendulum if
the whole mass were collected there. This point is called

* These immbers are taken from the Philosophical Magazine for
Peb. 1850. .

CLOCKS.

the eetUre of ascillatum. But it is not like the centre
of gravity, a fixed and independent point, for there is a
different centre of osdllation for every different centre of
suspension. It cannot be explaraed how the centre of
oscillation is found without reference to another imaginary
quantity called the radi/us of gyration. If M is the whole
mass of a body revolving or oscillating about any axis,
and i ia the radius of gyration about that axis, then Mi|=
the sum of all the elements m of the body each multiplied
into the square of its distance r firom the axis, which may be

expressed as 8 (*»/•*) ; and therefore i * = m '^^

som can only be found by means of the integral calculus
in every particular case. But there is this curious property
in revolving bodies ; that if we have once found the radius
of gyration k^ belonging to an axis through the centre of
gravity, then the It belonging to any parallel axis at the
distance A from the former one is given by this equation
i*=^J-i-A'. Suppose then that we know what ii is
for a body of any shape of which a vertical section in a

plane perpendicular to
the axis of suspension is
A B C D revolving round
its centre of gravity G,
and we make it revolve
or oscillate about a new
axis through S, and we
want to know what is
the length SO of the
equivalent simple pen-
dulum ; it may be proved

PENDULUM. 41

that SO = ii+|?! and /. GO = SO — SG = |1.

Prom this we may see also that if we draw two circles
round G, one with the radius S G and the other with radius
O G, we may put the axis of suspension anywhere in either of
the two circles and still the body will oscillate in the same
time. Perhaps therefore the radiu8 of oscillation would
be a more correct term than the centre of oscillation*

Now since S G = ^ it is evident that the nearer the axis

of suspension is to the centre of gravity^ the farther the
corresponding centre of oscillation will be; and this is
the reason why a small and delicate scale-beam will
oscillate as slowly as a pendulum many feet long; and it
also suggests a mode in which a pendulum might be mads
to oscillate veiy slowly in a small compass. If we make a
pendulum with two bobs^ one above and one below the
axis of suspension^ or take a wheel with a heavy rim and
suspend it on an axis a Uttle out of its centre, it may
vibrate two or more seconds in no greater space than a one
second pendulum; but such a pendulum will not be so
effectual in resisting the disturbances of the escapement as
a long pendulum of the same weighty which is what we
want a pendulum to do.

In all clock pendulums the effect of the weight of the
rod is to throw the centre of oscillation a little above the
centre of gravity of the bob, though below l;hat of the
whole pendulum; and by a few trials of the bob at different
heights the pendulum can be made to vibrate in the proper
time without the trouble of actual calculation. Now on
looking at the drawing of the cycloid, it is easy to see that

42^ . CLOCKS.

the ,o&abn 6t tnepeSimoii of anresd {i.e. not a s&ii|)ld) ^cxh
dulum swinging between cjdoidal cheeks is contiiraally
changing, and therefore the radios of oscillation is- con-
tinuaUy changiBg, and deviating from the length reqnired[
to describe the cycloidal arc. In other wordi^ a real pen^
dulum swinging in cycloidal cheeks is not equivalent to ^
rimple pendulum swinging in a cycloid, and therefoj* ii
not isochronous.

SUSPENSION OF PENDULUM.
26. Pendulums are now almost always suspended by

then swu^ without any friction; and they ate connected
with the axis or arbor carrying the pallets by a fork ot
ertUch, which is a light rod or ' aarm coming down bom th«
pallet arboif as if it was intended to'^be- the pendulum^
but ending in a fork whidh embrstc^ the penduhutf
tod ciosdy btit not so tightfy asi to jHre^ent the roci
from sliding wifliin itj so that thlfe pendulum and th^
crutch move tbgether, aAd the palfet arbor vibratei
as if the pendulum were hung ' directly to it in thd
iold way. It is to be observed; that as the spring does not
admit of being bent suddenly like a string, but assumed
a curved form as the pendtdum swings, its effect approaches
to that of the cycloidal cheeks. It has accordingly been
^attempted to make the spring of such a form and strength
as to render the vibrations of the pendulum isochronous ;
but without success; and it is of much more consequence
to find tiie spring which requires the least possible maintain-
ing force to keep up a given amount of vibration of the

SUSP£NSION OF PENDULUM. 4d

^iaid«lttm^ "^ieli is pidlubUy as tbixi a «pnp|^ as » stffefov^
&& weight' of tha petodoliun* t

f I am aii^ thdt smw^ experiments have bee^
tad lefaited to in the artide on dock^maUng, among iher
f nwrnnftiititafes/ in the JSny^lopadia MetropoUUma, hosni
whiehit would appear that a spring -008 of an inch thiol: af*
Sected tlie vibiatidns of a pendalum of 141hs.iireight less than)
any other spring of the same length and vidth, either thidcer
or thinner. I must say I should have had some difficulty m
believii^ that there was not some mistake in such a result^
from the thinner springs having got what is called a set in
fixing them (which is very likdy to happen with very thin
ones) or some other cause^ even if I had not been told also
that similar experiments have been made by other personswitb
the diffisrent and more probable result,* that the thinner th0
spriog) without limit, the less it ^ects the peodulum. And
as spinigs canno^ be nsed with safety of sndi thinness
hk paoportionrtb ^ weight of the pendulum. as that abova
qientionady we may in any case adopt theplacticalcdndosiom
that the thinneaf the spring is the less it will affect the peUti
dnliim/tUitiiiE^ tike less itarate wiU differ from a pendtilum
JMUgmg fiom an^aads of infinitdy small thickness*
i 27« It is of great importance that the real point ci
aaspenaiQn Df the peiidulum, that is the top of the spring
where it b^ins to bend, should be kept firmly in the same
place ; for if it moves it will increase the time of vibratiaDy
since this is evidently the same thing as if the fixed or real
point of suspension was a little higher up, or the pendului^
80 much longer. For this reason, in tl^ best docks, the
cock which carries the pendulum is a strong piece of brass.

4A CLOCKS.

or in large clocks a cast-iron firame^ firmly fixed to the wall
at the back of the clock. In order that the pendulum may
hang so that the spring will have no tendency to twist it as
it swings^ the top of the spring is pinched or 'dipped'
between two thick pieces of brass or iron called cAop^, and
firmly screwed there; and these chops have sqnare ends
exactly at right angles to a line down the middle of the
spring. A little way below the top of the chops, and
exactly in the middle, a strong steel pin is put through
them and the spring between them, at right angles to the
plane of the spring, and this pin has shoulders, so that
ita thin ends beyond the shoulders wiU jnst drop into two
nicks or Vs in the sides of the cock with the shoulders
resting against the sides. It is evident that the effect of
this will be that the weight of the pendulum will cause the
square ends of the chops, and therefore the top of the
spring, to be horizontal; and so, if the pendulum is made
symmetrically, as of course it ought to be, it will vibrate in
a vertical piano- at right angles to the line which is the top
of the spring, without any tendency to twist.

28. 'The two Vs should be made as nearly level as
possible, and the clock frame must be so placed that the
pallet arbor is exactly at right angles to the plane^of motion
of the pendulum. It will be easily seen if it is not, because
then the pendulum will sHde backwards and forwards in the
fork by which it is connected with the pallets. In the
chapter on church clocks I have given a drawing which will
show the suspension of a pendulum* In common clocks,
both house and turret clocks, the cock is fixed to the dock
frame, and has merdy a slit in it into which the spring fits.

PENDULUM SUSPENSION. 4S

having a piece of brass rivetted on to the top to keep it
from dropping through the slit. And this slit is very often
made so crooked^ or oblique to the axis of the pallets^ that
there is considerable friction of the pendulum sliding in the
fork; and the cock is generally made so slight^ and the
dock itself so loosely fixed to the clock case^ that the motion
of the pendulum may be plainly felt if you put your finger
on the clock.

KNIFE EDGES.

29. Occasional mention may be seen in books of
pendulums vibrating for several hours on haife edges ^ that is
on a suspension much like that of a scale beam. Such
a suspension is the best for experiments to ascertam the'
undisturbed time of vibration due to gravity only, excluding
the elasticity of a spring] but it is not to be inferred that
it will answer in practice for a permanent pendulum of the
proper weight for a clock ; for even if the knife edges and
the planes on which they stand are made of the hardest
stones^ it is foxmd that they soon suffer from the severe
pressure, and introduce an amount of friction which is fatal
to the accuracy of the pendulum.

PEICTION WHEELS.

SO. A suspension on friction wheels has also been tried,
but generally without success, the pendulum pivots always
wearing a hollow in the wheels; and then of course they
ceased to roU, and produced an amount of friction which
was fatal to the proper action of the pendulum, Mr. Y13I-

40 CLOCKS.

liamy, howerer, st&tea in the papers re^eoting the West-
minster dock, that the pendnhim of the dock at tlie ¥oBt*
office, which wdghs 4 cwt., has been goii^ erer sinee it wu
put i^ apon friction roOeaia ; that is to saj, npon so nmch
of an entire fdctioa vhed as is required for t^ small angle
thiongh which the pendulum vibrates. The arrangcmmt is
shewn in this drawings
The bearing feces of
these portions of fric-
tion wheds are not in*
deed made sensibljr cir-
cular, but are Sat pieces
of vay hard steel, with
certain provisions for se-
curing to tbe pivots a
flat bearing whidi it is
not neceasary to dra-
cribe ; but as tiie radius
of the pivots is only
l-150th of that of Ha
friction wheds, which
9&. 6in. Itmg, imd
the rollers only move
through an angle less
than 1' on each side ot zero, the versed sine or measure
of the curvature of a friction wheel for that angle is too
small a quantity to be expressed by a table of logarithms of
seven figures ; and th^efore {at all practical purposes the
bearings are the same as if Ihty were t^lindrical portions
-^ entir« &iotion wheels.

PENDULUM SUSPENSION. 47

Mr. Yulliamy tells me that bom the weight having
^been thrown almost entirely upon the pair of rollers nearest
to the pendnhim^ and the faces having been allowed to get
idirty^ it has been necessary to repolish them once lately. I
shonld be inclined however to make the pivots rather
thicker than *4 inch diameter for a Yerj heavy pendnlnm;
und the rollers should be placed nearer together^ becanse
the farther they are off the greater the pressure is upon
them, in ihe inverse ratio of the cosine of half the angle
included between them. It happens that for 60^, the angle
at which they stand in the Post-office dock, they have to
.bear just l-4th more pressure than the actual weight of
the pendulum. They would act at any angle safely above
that to which the pendulum swings : 20^ between them
wou]ld give them a sufficiently wide stride for a firm bearing
4nd add hardly anything to the pressure, and would also
reduce the tendency which friction wheels always have to
twist the pivots. The pivots here are not indeed common
.projecting pivots, which would be too weak, but a hard
^iece of turned steel .bedded into a strong beam, to which
the pendulum is hung, and to another part of which the
.pallets ace fixed.

The advantages of this method are, that there is no
necessity for any ccnnpensation of the spring ; which how-*
ever, as will be explained under 'compensation of pendu-
lums,' requires only a small addition (though of rather unoer-
.tain amount) to the ordinary compensation required for the
.expansion of the rod. The risk of a spring breaking is too
,jrare an accident to be worth enumerating as an advantage of
jUus snspensioi^; and it can be repaired in an hour when it

48 CLOCKS.

does happeiL The principal advantage of it probably
is that it enables the pallets to be put on the arbor
which carries the pendnliun, or in other words dispenses
with a crutch, and therefore prevents the loss of force
which must always (though to a small extent) take place
in the transmission of the impulse through the crutch, both
by the friction and the shake in its pivot holes ; and we
shall see that everything that dbninishes this force, and
therefore requires a stronger pressure on the pallets, m*
creases the chances of error in the going of the clock.

No doubt even the small amount of rolling Mction
in this suspension would destroy the motion of a free
pendulum sooner than a spring: but the proper com-
parison to make is between a common pendulum with
a spring and crutch, and this without a crutch. I
have no means of stating the result of such a com«
parison, either as to this point or the performance of the
same clock with the two different pendulums, which I
should require to be tried before I would undertake to
recommend such a suspension, Mr. Vulliamy however teUs
me that the Post-of&ce pendulum was kept vibrating 2** 22',
with only a weight of 30 lbs. falling at the rate of 47 feet
in the 8 days (the dial work being unattached) ; which is
tm unusually small weight and fall for a large clock; and
I must say (with the reservation just now made) that
I think this fact is of much more importance towards
determining the actual merits of the plan than the
astronomer royal^s inference, in his report upon the plans
for the Westminster clock, that it would fail because he
^ knows that it would f^ for a balance or a vertical-force-

VEETICAL E8CAEEMEKT. 49

magnetometer:' on which it is very obrioaa to remark
that knife edges are the only things that imawer for a
balance, and 7^ they invariably £ul under the continaed
pressure of a heavy pendnlmn. I need hardly say that this
mtspenaion most be very expensive, and votdd require the
greatest care in properly constmcting and adjusting.

31. Long after pendulums were invented, tiie vertical
escapement continned te be used, in the fonn in which
I have Buggeated that Harris may have invented pendulum
clocks; and snch clocks are still in existence. The arrauge-
. ment is that shown in this drawing, a second crown wheel

80 clocks;

being' used in order to keep the arbors ol all the wheebi
except the scape wheel horizontal. A wheel of this kind
is sometimes called a cotUrate wheel; and its teeth and those
of the pinion which it drives> onght properly to be of the
sihape required by two conical or bevelled wheels of the re*
spective sizes of the wheel and pinion. In practice, how*
ever, the pinion being small is made cjlindrical as nsnal,
and the teeth of the contrate wheel being thin, they work
together ^ sufficiently well for the work in which they are
employed, such as vertical watches. Clocks with this
escapement however have been quite superseded by the
invention of ' ^

ANCHOB PALLETS.

32. These are said to have been invented either by Dr.
Hooke, one of the most scientific men, and probably the
greatest inventor of the 17th century, or by Clements, a
London clockmaker. It will be at once understood from
this drawing what they are. [See next page, "] The bottle-
jack or 'vertical' pallets, being close to their axis of vibra-
tion, required the pendulum to move through a large arc
in order to clear the teeth of the scape wheel; and besides
what we have seen of the disadvantages of large arcs, thqr
require a larger maintaining power than small ones. In
this drawing a tooth, a is represented as having just escaped
from the pallet A, and a tooth b on the opposite side of the
wheel has dropped on to the pallet B. The pendulum will
not however stop here, but will advance a little further to
the left, and so the slope of the pallet B will drive the tooth
h bacj: again a little and produce the recoil, which may be

ANCHOR PALLETS. 51

observed very plainly
in any common honse
clock with a seconds
hand. The sloped
&ce of the pallets
Causes the teeth to
give th«n an impulse
in escaping, so as to {
maintain tte motion '
of the pendulum.
This kind of escape-
ment is much the
most common, and
will probably never be
superseded, as it is
sufficiently accofate
for ordinary purposes,
,and is very easy to
make, siiice no p^-
tictdar form is requi-
red for the pallets.

Their acting faces are generally made fiat ; but they are
better convex, as in the drawing, as ^ere is then less recoil
and less wetuing of the pallets by the points of the teeth.
Strange as it seems that brass teeth should wear boles in
steel made as hard as it can be tempered, it will always be
found that the teeth have worn boles in these pallets after
a few years, and the hole will be deepest towards the end of
the place which the tooth resiches. It is evident that the
tendency to make this hole will be less if the pallet is cou-

52 CLOCKS.

vex than if it is flat; and accordinglj in the best clocks of
this construction the pallets are so made ; and care should
also be taken that they are so placed that the recoil and
the drop may be equal from each pallet. The recoil escape-
ment is now abandoned in aU the best clocks, though it
once had considerable persons as its advocates, who appear
to have been misled by observing that it keeps the pendulum
to the same 4irc more than the dead escapement does, and
thence inferring that it would keep it more nearly to the
same time; whereas it is now proved, both by experiment
and calculation, that although, as the force of the dock
diminishes from increasing Unction or thickening of the oil,
the arc will diminish, the clock will nevertheless lose ; the
loss caused by the escapement being more than enough to
counterbalance the .$gain due to the circular error of the
decrease of the arc. . The same is the case with a watch
liaving a vertical or a recoil escapement.

DEAD ESCAPEMENT.

33. The escapement which is now used in nearly all
astronomical clocks and in all good turret clocks is called
the dead beat escapement, and was invented by a clock-
maker of the name of Graham in the last century. A
recoil escapement would be converted into a dead escape-
ment by making the slope of each pallet stop at the
points A and B where the teeth fall, and making the rest
of the pallets A D and B E portions of a drcle whose centre
is C the axis of the pallets. Eor in that case, however far the
pendulum may swing no recoil can take place. The reason

DEAD ESCAPEMENT. &3

vhy this escape-
ment ia 80 much
better than the
retbil escapement
is, that a variation
in the force of the
dock train pro-
duces hardly any
effect upon the
lime of oscillation
of the pendulum,
thonghitproduces
a considerable ef-
fect upon the ez-
ieak of its oscil-
lation.

84. This may
be shown in a ge-
neral way as fol-
lows. Let c be

Uie angle which the pendulum rod makes with tlie
T^ical o when a tooth begins to act on the sloped &ce
of the pallet, c' the angle on the other side of the vertical
at which the impulae ends or the tooth escapes. Theo-
retically c and c' might be equal, but practically c' must
be a little lai^er than c, in order that the tooth may not
drop exactly on the corner of the pallet but just beyond it
on the circular or dead part. Now while the pendulum is
descending from c down to o the force of the clock acts
in the &ame direction as gravity, which is the same thing

54: CLOCKS.

«s if the force of gravity, or the earth^s attraction, were
increased by a certain amount; but while the pendulum
ascends from o up to c', gravity may be considered as
diminished by the same amount (assuming the force of the
clock to be constant throughout) ; and therefore on the
whole the two disturbances would balance each other, but
for the fact of c' being rather larger than c, and as the
tooth evidently makes a larger angle with the pallet towards
the end of the impulse than at the beginning, the force is
not quite constant throughout, but a little greater through
c' than through c ; and therefore on the whole the force
of gravity may be considered as a little diminished, and
the pendulum will vibrate a little more slowly than if it
were free from the clock ; for it is evident that if the
attraction of the earth were weaker a body would fall, or ^
pendulum vibrate, more slowly, as the time of the ascent
is always equal to that of the descent. It is also evident
that as the force acts throughout in the same direction
as the pendulum is going, it must increase the arc of
vibration.

S5. Moreover the uniform friction on the dead part of
the pallets hardly affects the time directly; siace from the
extremity of the descending arc down to c? it acts contrary
to gravity, and from c' up to the end of the ascending
arc it acts with gravity, but as it always retards the pen-
dulum of course it diminishes the arc. On the other hand,
in the recoil escapement the action during the middle part
of the oscillation is the same as in the dead escapement,
but towards the extremities of the arc the force acts with
gravity not only in the descent of the pendulum, but also

DEAD S8CAPEMENT. 55

ill lis ascent daring the recoil; and therefore my increase
of the force will make the pendulum swing faster^ though
at the same time the arc is increased by the action through
the middle of the oscillation as in the dead escapement^ and
is not affected by the action at the extremities of the arc.
The difference between the time of oscillation of a pen-
dulum attached to a dead escapement and xmattached
!>eing very small, the second difference, between the times
)f the same pendulum with different degrees of force in
tie escapement, must be exceedingly small; which accounts
for the accurate 'performance' of clocks with this es-
capement.

86. This kind of reasoning however will not enable us
toietennine the actual amount of the errors arising from

any particular amount of change in the force, or in the
arc. The calculations necessary for obtaining these results
are loo complicated to be introduced here, but the results
thenselves are sufBlciently simple. Let D be the difference
in tventy-four hours between the time of the da/s os-
cillations of a free pendulum and the same number of
oscilkions of a similar pendulum attached to a clock with
this esmpement ; a the angle of vibration on each side of
zero; f the angle at which the impulse begins, c' the
angle on the other side of zero at which it ends; W the
clod weight, and A its fall in a day, M the weight of

the pendulum, and I its length; then it may be proved

"VTA «'-— c
that D =T77" Q^ — i very nearly, provided that cf and c are

not huger than about -r • Suppose for example ^ to be
2°, ani </- c = 20', W = 2 lbs. and >l = 9 inches (which.

5^ CLOCKS.

though less than rumal^ is 6u£5[Gieiit for a highly finished
clock with light wheels)^ M =s 14. lbs. and ^ = 39 inches ;
then D wiU = .8 of a second.

But it must be r^nembered that the daily error in the
going of the clock is not D, bnt the poritUion of D due to a
given variation in the force which arrives at the escapement,
and to the change in the arc of vibration^ which will vary both
from changes in the force and the friction on the dead part
of the pallets. Now if the force of the clock is increased by
a small amount d Vf, and the corresponding change in the
arc is called da^. then it fdllows> on the principles of thi
differential calculus^ that the increase of D, or

To this must be added the circular error, which va
found to be (assuming it to be entirely uncorrected by tie
pendulum spring) 10800 o/fo. Therefore the whole daily
loss of time will be

,T~r -^ — a 1^;;;^ l + 10800 ada.

If we took the friction on the dead pefft of the pdlets
into account, we should introduce anoth^ small term
showing a farther increase of time, and depending /upon
the pressure on the pallets and the coefficient off'hcUon,
or the ratio of the friction to the pressure (which is idd to
be from I to -jiy between weU polished and oiled siirftces
of brass and steel), and also depending like the other/ on
d —c. Both for this reason, and because the dead fri<tion
diminishes the arc of vibration, the effect of which weBhall
see presently, it is by no means to be taken for gifted
that, because a constant friction on the pendulum through

DEAD ESCAPEMENT. 57

equal angles on each side of zero produces no direet effect
upon the time of a vibration, therefore the friction in the
dead escapement on the circular part of the pallets does no
hann. We shall see a remarkable proof of the extent
to which it diminishes the ability of the pendulum to
resist the other disturbances, in an escapement (47) in
which these other disturbances are much reduced, while the
dead friction is much increased. Indeed it is obvious
without either calculation or experiment, that the more
friction there is, the larger must be the impulse required
to make up for it, and consequently the larger wiU be all
the errors connected with the impulse.

37. We see now the true cause of the accuracy of the
dead escapement, and also how we are to set about it, to
make this accuracy as great as possible. For though we
camiot determine the proportion which the increase of the
arc bears to that of the force, since it depends upon the
varying friction of the different parts of the clock, yet we
see that they have a tendency always to correct each other ;
and whenever the state of the clock is such (as in one
experiment I actually found it to be) that the arc increases
just one-third as much as the clock-weight is increased,
those two parts of the error will exactly counteract each
other : and the ratio of the increase might happen to be
such as to compensate the circular error also. It generally
happens, however, that as the clock gets dirty, the force
and the arc decrease in such a proportion that the loss of
time preponderates.

But there is one case in which the opposite effect
not unfrequently takes place to the surprise of those who

B8 CLOCKS.

know the common result of a decrease of arc, and of
which for some time I could not myself discover the rea-
son. Church clocks will often be found in a few months
after they are put up to increase their arc of vibration con-
siderably, and at the same time to ffain. This increase of
arc arises chiefly from the decrease of friction on the dead
part of the pallets, owing to the teeth and pallets polishing
themselves more perfectly than had been done by the
maker. Moreover in most clocks the quantity that we
have called D is much larger than in the above example ;
and therefore the terms depending on D are much larger
than the term containing the circular error. Consequently

the term D may preponderate over both the. other

terms ; and as it has a — sign the clock wiU then gain
while the arc increases.

It may be as well to explain that when a clock gains it
is said to have a + daily rate of so many seconds, and.
when it loses, a — rate; and it should be remembered that
these §igns are the reverse of those which indicate the
decrease or increase of the time of an oscillation. I may also
remind the inexperienced reader that the goodness of a
clock is indicated, not by its rate, but by the variation in
its rate.

38. The effect which I have just now mentioned, pf the.
self-polishing of the pallets is of course only temporary ;
and the general effect of a decrease of force and of arc in a
4ead escapement is, that the clock gains a little, whereas a
common recoij escapement loses considerably as the arc
decreases; and this has led,, to the ado^ion of a smaU
recoil in the place of the dead part of the pallets, especially

HALF-DEAD £SCAPBM£NT.

in turret clocks^ whicli are more liable to changes of
friction than others. This recoil may be given hj striking
the circle of the dead part of the pallets, not from the axis
of the pallets, but from a point a little below that axis, in
the line of centres of the pallets and the scape-whed, which
produces a circle with a higher degree of curvature, and
therefore raises the teeth a little after they have dropped
onto the pallets: and the farther the pendulum swings
the greater is the degree of recoil. This is commonly
called .the half^dead escapement.

89. There are some other things to be learned from the
above expression for the daily error of a dead escapement,
and some of them apply to all escapements. First, we
observe that, as the weight and length of the pendulum are
ia the denominator of the. fraction, the larger they are the
less the errors of the clock will be; and this is the case
with all escapements, and with all the errors, Whether of
friction or anything else, connected with the escapement;
for it is quite a vulgai j^rror to suppose (other things being
equal) that a heavy or long pendulum requires a heavier
dock weight than a short and light one, except that of
course in large clocks the pendulum spring is stiffer, and
the whole of the machinery heavier, and so requires a
larger weight to move it than in small ones. The best
turret clocks have 2, or 1^ seconds pendulums, which are
about thirteen and eight feet long respectively, and the bob
sometimes as much as four cwt. Now if the same clock
had a one second pendulum with a bob of half a cwt.,
instead of a two seconds pendulum with a bob of four cwt.,
it would go just thirty-two times worse ; or in other words,,.

60 CLOCKS.

if with the long and heavy pendulum it varied a minute in
a months with the other pendulum it would vary above half
an hour.

40. The next independent quantity in the equation far
B or dJ) is (/— c, or the diJBferenee between the angle at
which the impulse begins and the angle (on the other side
of zero) at which it ends^ which is called the af^le of
escape. And we see that the smaller this difference can be
made the smaller all the errors of the escapement will b^
as indeed was apparent from the general reasoning inde-
pendently of the exact value of D. The limit to the
smallness of d-^c is merely a practical one, depending upon
the accuracy of the construction of the escapement, and
upon the length of the pallets (by which I mean the arms
that carry the pallets), for of course the longer they are the
smaller will be the angle c^—c corresponding to a given
linear space required for the tooth to fall upon. The
length of the pallets can only be varied in two ways ; either
by increasing the wheel and pallets together, or by in-
creasing the number of teeth which the pallets embrace.

41. But it is to be observed that as you increase the
length of the pallets you also increase the linear space over
which all the friction acts, both the friction during the
impulse and the dead friction ; and if the wheel remains
of the same size, the pressure, to which the intensity of
ihe friction bears a certain proportion, will be the same ;
aad so the total quantity of the friction will be increased
by increasing the number of teeth embraced by the pallets
in order to increase their length ; for the radius of each
pallet, drawn from the pallet arbor to the comer of the slope.

BEAD ESCAPEMENT. 61

must be a tangent to the circumference of the teeth of the
i^cape wheels in order that the teeth on each side may act
equally^ and for the same arc of the pendulum^ upon the
slopes of both the pallets. The pallets therefore are seldom
made to embrace more than the space of 10| teeth^ or 11^
at the most^ when the wheel has thirty as usual.

4t2. Again it is not desirable to increase the size of the
wheel beyond what is necessary for its proper strength in
proportion to the number of teeth, because its moment of
inertia increases even more rapidly than its size, and so
causes it not to follow the pallets so quickly : and when
tithe wheel is too large, the teeth may often be heard to
jump or chatter on the pallets, from the length of the drop
land the great Hnear velocity they have acquired when they
are suddenly stopped. In astronomical clocks, or 'regulators'
as they are called, the scape-wheel is generally two inches
in diameter or a little more, and cf^-c can be made as little
as £0' and ought never to be more than 30'. In turret clocks
five inches is quite enough for the diameter of a scape
wheel with thirty teeth ; and as that will allow more than
twice as much linear space to the same angle as a wheel
only two inches in diameter, c'— c, may be made as little as
in a regulator. I have improved the going of a church
clock, which was very weU made in other respects, by opening
the pallets wider, as they had been so set that the tooth
fell on the circular part a good way above the slope, in-
stead of as near to it as possible; and they fortunately
admitted ef adjustment.

43. I have said nothing about the size of tZ-f c as well
as d—c, because that quantity does not enter into the

52 CLOCKS.

value of D. But it is evident that the larger these angles
are, the longer the impulse will last and the less dead
friction there will be for the same degree of oscillation; and
also the less suddenly the teeth have to drop, and conse-
quently the more closely they will follow the pallets at the
beginning of the impulse. But on the other hand the
friction occurs during the impulse instead of occurring on
the, dead part; and the question between long and short
impulses is one which is perhaps better determined by
eKperiment than theory; the result however both of theory
and experience seems to be in favour of a short impulse^
especially as it requires a less arc upon the whole, and less
maintaining force. Mr. Dent makes d^ the larger of the
two angles not much above half a degree, and the angle of
oscillation 1|° in his astronomical clocks, and some of them
are going with only a weight of four lbs., and the pulley,
faUing three feet in the eight days. A clock of this sort
is also . Bafer than one in which the angle of impulse is
nearly equal to the whole arc of vibration, for in that case
a little diminution of the arc &om any accidental cause,
such as freezing of the oil, will cause the clock to stop.
This was what the old dockmakers meant when they said
that the excttrsion, or the excess of the anglp of vibration
above the angle of escape, ought to be large.

44. There remains to be noticed one other ingredient in

the equation for D, viz. — r; for these quantities evidently

depend on each other, as you cannot increase the arc in a
given clock, but by increasing either W the clock-weight, or
A its fall in the day. As was observed before, it is impos-
sible to say practically what increase of arc ^ a any given

DEAD ESCAPEMENT. 63

increase of WA will produce ; but it is certain that the arc
increases much more slowly than the weight ; and^ moreover^
as the arc is increased, the quantity of dead friction is in-
creased; and, therefore, on the whole, it is found that no
good is done by adding to the weight in order to increase
the arc. (This remark will not apply to the next class of
escapements in which there is no dead friction.) But if
you can increase the arc by diminishing the friction on the
pallets, or improving the suspension of the pendulum, that
is a clear gain; and accordingly the less weight and fall a
dock requires to make the pendulum vibrate a given arc
(other things being equal), the better the clock will go.
For this purpose the pallets ought to be made as hard
as possible ; and in highly finished clocks they are made of
j.ewels ; sapphires I understand are the best. It seems to
be a question whether steel or brass teeth work best upon
jewels : upon steel pallets there seems to be no doubt that
brass teeth work with less friction than steel and require less
oil ; but the brass should be hammered so as to make it as
hard as possible.

45. Various contrivances have been proposed for di-
minishing the amount of dead friction, such as having
separate pallets for the dead part of the action, which are to
be left behind by the pendulum as it advances beyond the
angle of escape (c/), and carries the impulse pallets with it.
It will be seen, when we come to renwntoire escapements,
why this plan is objectionable, besides the difficulty of con*
structing it. Perhaps it might answer to put a large and a
small scape- wheel on the same arbor, and short and long
pallets on the same pallet arbor, the small wheel to give the

DUPLEX DEAD ESCAPEHEKT.

impnlse on the long pallets, aod the teeth of the lai^ whed
to be stopped by the
Bhort palleU contain-
ing only the dead
part, which however
is to have a small re-
coil in it. Inthatcase
the impulse might be
given throngh a small
' angle n&a the middle
of the vibration ; and
the presaate which
causes the dead fric-
tion wonl^ be less
from a lai^e wheel than a small one, and the space to be
travelled over on the dead part of the short pallets wonid
also be less than on long pallets; so that iu every way
there would be an advantage as r^ards Miction. This may
be called a di^Ux escapement, as it agrees with the escape-
ment of that name in watches. It would lequire con-
siderable accuracy in its construction, bat not more than
mother, which I shall mention presently, as having been
constructed, and at work.*

46. There is mother form of the dead escapement,
which does not differ in principle from the common one,
but has some mechanical advantages over it, espedally for
U^e clo<^. It is called the j»»-w^e/ etcapement. It will

• I hare made thia and several other drawinga in this book mote
with a view to an intelligible exhibition of the action of the puts,
than to their aetiuJ at proposed oonatrnction.

DEAD ESCAPEMENT. 65

be snfQciently clear from the drawing, that the pins are set
on the face of the
scape wheel in-
stead of teeth on
its edge, and that
the two pallets,
instead of embra-
cing about one-
third of the cir-
cnmference of the
wheel, are pat so
near together as to
leave roomforonlj
one pin to pass
between them ; and
the end of one

slope shonld be just over the beginning of tiie other.
The pins are only semi-cylinders, since the npper part of
the cylinder could not act, and cntting it away allows 1^
pallets to slip throngh close above the teeth, so as to waste
as little drop as possible. The advantages of this escape-
ment are, first, that it does not require so much accuracy
of construction as the oth^; for in the common one if every
tooth is not exactly in its right place, with reference to eveiy
other at the distance of ten or eleven &om it, the escape-
ment is liable to stick, and if the clock is going with a
heavy pendulum a tooth is then pretty sure to be broken ;
whereas if every successive pin in the pin-wheel escapement
is neaily at the same distance from the one immediately
before it they are sure to cleat the pallets : secondly, if by

66 CLOCKS.

any accident a tooth of the common scape wheel is broken
the wheel is ruined ; whereas if a pin is broken a new one
can be put in in a few minutes : thirdly, many more pins
can be put into a wheel of given size, so as to clear the
pallets, than teeth of the usual shape ; and therefore there
is less drop and waste of power at every beat,* and the
wheel turns through a less angle and with less velocity,
and therefore with less friction on its pivots, and can also
have a larger number of leaves to its pinion^ the advantage
of which will be seen when we come to consider the wheel
work : fourthly, both strokes on the pallets being down-
wards, instead of one downwards and the other upwards,
there is less shake in the pallet arbor; in a common escape-
ment the difference of stroke on the up and the down
pallet can generally be distinguished by the sound.

The only disadvantage of this escapement, as for as I
know, is that the force of the cylindrical pins on the palleta
is not so uniform from the begmning to the end of the
impulse as with sharp teeth and pallets with straight slopes;-
in fact, the slopes ought strictly to be concave, in order to
make the inclination of the tooth to the pallet the same at
the end as at the beginning of the impulse. This however
oould not be done without the introduction of greater evils
than the very small variation in the force. The pin escape-
ment has been long used by the best makers of turret
docks both here and in Erance. It is not used in
the Exchange dock, because it is not so well adapted for
jewelled pallets, which that clock has. Mr. Yulliamy
makes the pins of steel acting on broad pallets, portions of
turned cylinders, and without any recoil ; diminishing the

DUPLEX SPRING ESCAPEMENT. 67.

radius of the cylinder^ or setting the same pallets on longer
arms^ would give them a small recoil. Mr. Dent uses hard
bra^s wire pins acting on pallets, not flat, but having the
cross section a segment of a circle, and he makes the escape-
ment ' half dead.' The scape-wheel for a 1 ^ sec. pendulum,
with forty pins in it, in the two clocks I shall mention, is not
quite four inches in diameter ; this shows the small amount
of drop which this escapement requires compared with the
c(»nmon one;

ME. AIRY'S DUPLEX SPEING ESCAPEMENT.

47. Before I proceed to the next class of escapements,
and by way of introduction to them^ I will describe the one
I alluded to just now, which was invented by the astronomer
royal, and of which three or four specimens have been
made by Mr. Dent : one of them is now going in his
shop in Cockspur-street. In order to prevent the inequali-
ties of force of the train affecting the impulse on the pendu-.
lum, there are two scape-wheels and two pairs of pallets,
one for the stop, and the other for the impulse : the stop-
wheel is the one connected with the train, and the impulse-
wheel rides on the same arbor, and is connected with the
other by a spiral spring. The stop-wheel is let go by its
pallets, which have no sloped £aces, just before a tooth of
tiie impulse-wheel would arrive at the slope of its pallets^
and so the tooth is carried down the slope, and the impulse,
given by the force of the spring only. In fact, if the reader
turns to the drawing of the duplex escapement in page 64,
and supposes those two wheels reduced to the same size,. and.

68 CLOCKS.

connected by a spiral spring instead of by screws, it will re-
present this escapement (which I may observe is not the one
suggested by Mr. Airy some years ago in his paper in the
'Cambridge Philosophical Transactions^). The advantage
of it is that the impulse is constant, or at least has no
greater variation than that of the force of the spring arising
from changes of temperature, which is much smaller than
the variations in force caused by the friction of the train ;
with however this not immaterial exception, that the
impulse-wheel tiims with more friction, riding on the arbor
of the other wheel, than if it turned on pivots as usual.
Moreover the dead friction is that due to the train, and
is very much greater than usual. The reader may form
sameTome idea of the amount of force consumed by this
friction and the additional weight of the second scape-
wheel, when I state that (reducing the falls to the same
amount) the weight employed in driving this clock is more
than twice as much as that employed in driving one of Mr.
Denf s second-rate regulators, vibrating the same arc, and
more than three times the weight of one of his first-rate
regulators, also with the same arc; notwithstanding the
numbers of the pinions of the clock with the duplex escape-
ment are higher than those of either of the others, and the
dock is made with the utmost care. And it is not sur-
prising that this large amount of friction more than coun-
terbalances the advantages of this escapement, and the
dock does not go so well as a first rate regulator with the
common dead escapement. Both these objections might
probably be diminished; the first by making the stop whed
ride upon an arbor or stud set on the frame, and carrying the

REMONTOIRE ESCAPEMENTS. 69

pivot of the impulae wheel in the maimer I shall have to
describe in a chnich clock lately made according to some
sn^estions of my own (177) ; and the second by n9ing a
large and light stop-wheel with short pallets in the manner
above described (45).

BEMONTOIKE ESCAPEMENTS.

48. Escapements of the kind jnst now described^ (so
far as the impulse wheel is concerned) in which the impulse
is given to the pendulum by a small separate weight or
spring, independently of the force of the train, are called
by the Erench remantoke escapements, because the clock
train winds or lifts up the maintaining force at every beat
or at some given number of beats of the pendulum. They
have long exercised the ingenuity of clockmakeis; so
long indeed and generally so unsuccessfully^ that they
appear to be considered by some people the philosopher's
stone, or the perpetual motion, of dockmaking. It would
be impossible to describe in any reasonable compass the
various inventions that have been made for the purpose,
both for clocks and chronometers. Eor chronometers they
have always hitherto faUed, and I have no doubt they
always will; not only on account of the excesssive trouble
and difficulty of constructing them on so small a scale, but
because a chronometer train is so ]ight that there is npthing
like the same friction and waste, and therefore variation, of
force between the main-spring and the scape wheel as there
is in clocks, especially turret clocks, for which remontoires
are most required. But that they can be made and ill
answer for clocks, both large and small, is fully proved by

70 CLOCKS.

Mtmul examples of them which I shall describe as actually
now at work with complete snccess, hesides the one which
I JDBt DOW described and which may be considered an
ewiq)ement of the ' transitioii style' between dead and re*
montoire escapements, or rather between an escapement
remontoire and a train remontoire.

49. When the impulse is given to the pendulum by a
■mall weight or weights, instead of a spring, raised at every

GRAVITY ESCAPEMENT. 7t

beat or other int^rval^ thej are called gravity remontoires^ o)r
merely gravity eacwpemmU.

The most simple^ though not the earliest form of the
gravity escapement is this. A G^ B C^ are two arms turning
separately, on pivots at C which coincide as nearly as
possible with the axis of suspension of the pendulum:
At the lower ends of the arms are two pallets of the shape
in the drawings so that a tooth of the scape wheel will
slide along the sloped part and raise the arm until it comes
to the little detent or hook at the end^ which stops the
tooth : the tooth at B is here represented as stopped^ and
the tooth at A reieuly to raise the arm A€^ as soon as the
other arm. is pushed farther out so as to set the wheel free.
The arms liave projecting pieces, D, E, reaching down to
the proper distance to be met by the pendidum rod. The
pendulum is here drawn as going to the right and just
touching the projecting piece E of the arm B C : as the
pendulum goes on it will raise that arm and set the
wheel free to raise the other arm; and the pendulum
will carry the arm BC with it as far as it swings, and
when it descends again the arm will descend with it,
not only as far as the place where it was taken up, but
farther, that is, until the slope of the pallet B rests upon
the next tooth of the wheel, or upon some fixed stop set in
tiie frame at the proper height. The maintaining force
upon the pendulum depends therefore, first, upon the
weight of the arms, and secondly, upon the difference
between the angle of the pendulum when it takes up each
arm in ascending and leaves it in returning. If the arms,-
instead of. acting by their own weight, were so counter-^

72 CLOCKS.

balanced that their weight did not act upon the pendnlnm^
and were fixed b j short and rather stiff springs like a
pendulum spring at C, the action would be evidently just
the same, only it would then be a ^prinff, instead of a
gravity remontoire; and if not counterbalanced, it would
be a compound of the two.

50. This simple form of the escapement will do as well
as any other to ei^lain the general advantages, and the
mathematical conditions to be observed in the construction
of all these escapements, whatever may be their mechanical
peculiarities. The advantages of them are evidently these :
first, the impulse depends upon the action of a given
weight pressing on the pendulum through a given distance
(that is a given difference between two distances) and
communicated without any friction, except the incon-
siderable friction of the pivots at G ; the force is therefore
independent of all variations in the friction in the train
and escapement. Secondly, there is nothing corresponding
to the dead friction of the dead escapement, or the still
greater friction of the recoil escapement; and therefore the
pendulum will be much less liable to variations in its are
of vibration : indeed there is no friction at all except the
momentary friction of unlocking the teeth when the pen-
dulum first catches the arms ; and therefore the pendulum
will swing a given arc with less nudntaining force. A
third advantage has been supposed to be that the pendulum
may be leffc quite free for some distance during the middle of
its arc, since it need not be nutde to take up one arm as soon
as it leaves the other : this however we shall find to be the
worst construction, though it has been the most common.

EEMONTOIRE ESCAPEMENT. 73

51. Now if we could be sure that the pendulum would
never vary at all in its arc, this escapement would be
mathematicallj perfect. But there is no such thing in
practical mechanics as perfectly invariable motion ; and it
unfortunately happens that if the arc of vibration varies at
all, from change in the density of the air or the little
friction which exists, it produces much worse effects with
this escapement than a much larger variation of the arc
produces with the dead escapement. Por as was shown in
the recoil escapement, the additional force, or weight of the
arms, acts with gravity both in the ascent and descent of
the pendulum, and therefore the farther it ascends with
this additional force acting upon it, the more the time of
its oscillation will be diminished. In order to show the
amount of this acceleration, let D as before be the' increase
of the time of aU the oscillations of a seconds pendulum
in a day when attached to this escapement : c the angle
(from zero) at whict the pendulum takes up each arm, c^
the angle at which it leaves the other arm ; only you must
remember that d is now supposed to be on the same side
of zero as c, and not on the opposite side as in the dead
escapement ; "W, h, M, l, and a, indicate the same things as
in the dead escapement. Then it may be proved that

The — sign indicates that D is here a decrease of time
instead of an increase, c and d may be any angles we please,
except that d must be less than c, or there will be no
impulse given to the pendulum, and also c cannot safely be
more than a — 30', since the unlocking of the wheel has

74 CLOCKS.

to take place while the pendulum is moving through a^-^e.
It will be found that whatever value of c— (?* we take,
subject to these conditions, the value of D in this escape-
ment is many times greater than in the dead escapement.
And since D is so much larger in the remontoire than in
the dead escapement, it was perhaps natural to suppose
that the variations of D (which are the error of the clock)
must be larger abo; akd experience was supposed to confirm
this theory, for however carefully the remontoire escape-
ments have been made, they have not generally equalled
the accuracy of the dead escapement, and when they have,
only by their mechanical advantages and veiy perfect con-
struction.

62. But although this conclusion would be perfectly
correct if applied to any construction of the remontoire
escapement which a clockmaker would spontaneously adopt
(which accoTmts fot experience appearing to confimi theory),
there is nevertheless a construction, wliich, though not
very convenient^ is quite practic^-ble, and will render the
variations of D so small as to be inappreciable for any
probable variation of the arc of vibration. In order to
produce this effect, it may be proved that <?, d^ and a must
be made to satisfy this condition :

Many different values of c and d for any given value of a
will theoretically satisfy the equa,tion ; but practically the
number-is very limited by the circumstances mentioned a
little while ago. For suppose that we intend a to be 12(K
and ff to be on the same side as c; then in order that a — e

bemontoibj: escapement. 75

may =£ 80'^ c must not be more tha^ 90'^ and we shall find
that the corresponding value of ^ is very nearly 78'. But this
construction is barely practicable^ for the angle through which
the impulse has to be given^ and through which the arms have
to be raised by the escapement will be only 12', and these
small angles are extromdy difficult to manage with a<^uracy
in the construction ;9f the escapement. Probably the only
way in which it can be done is by such a construction as
that which many persons must have seen in the window of
Mr. Denf s shop, made^ however, without any reference to
this theory, in which the action takes place near the bottom
of the pendulum, and so the linear space corresponding
to a small angle is sufficiently large. This construction,
however, is on another account very inferior to that in
.which e and </ are on opposite sides, or the arms act upon
the pendulum through a considerable angle on each side of
sero; as may be seen at once from the fact that, in that case,
e — (f, which occurs in the denominator of the value of D and
its variations, becomes e+(f, and therefore the value of
D and dD is very much smaller than when c and cf are
on the same side of zero, or the pendulum is free in the
middle of its swing.

SS. Suppose then that e and {/ are on opposite sides, and
a=120' as before; then one construction that will answer

is to make c and & each =-^ or 84'* 86, so that one arm

is always taken up just as the other is left. And as it
is not safe to allow the pendulum to touch one arm before
ihe other has reached its lowest point, and is ready to catch
the scape-wheel, any value of </ larger than c is practically
inadmissible ; and on the whple the best form of the remou-

76 CLOCKS.

toire escapement evidently is that in which c and ^ are on
opposite sides of zero, and each = y^ or *707a. In that
case the equation in § 51 assumes the more simple form,

and the variation of D toi das, given small variation of a,

,T. Wh a* da

M/iTfl* /^ , a

Now in order to see what the ^ror of such a dock will
amount to for certain small variations of the arc, we may
put for W^ half its value in the deadeseapement, as that is
sufficient for a weU-made clock of this sort, there being no
dead friction to overcome ; and as a = 120' and therefore

c = 84'-86, or -0246, m71^ = ^'^ > ^^ ^® shall find
that if a increases or decreases from 120' to the followiog
amounts, the clock will in either case gain, but no more than
the following small quantities daily :

a = 123' dD = Yh ^^ ^ second

122' ^

120'

118' ^

117' ^

Therefore as the arc will never spontaneously increase,
it should be so adjusted when the pivots and pallets are
cleaned, that a may exceed the normal value by a little more
than 1', which it will do if the pendulum is made to swing
to 120' in a clock in which c is 84'; and then the arc
may diminish as much as 4/ or 5' without producing any

BEMONTOIRE ESCAPEMENT. 7T

aensiblQ effect upon the rate of the dock ; and sach a clock
may be pronounced theoretically perfect.

If c should be made a more convenient size^ say 1^ for
a = Z^, the clock will lose for an increase and gain for
a decrease of arc : but it will only lo^ 4- of a second a day
for a decr^ oi 5', wHch is a very large variation of
the arc for such a dock ; and^ therefore^ even with this con-
struction^ it would probably go better than any dead escape-
ment. These escapements have however, I believe, been
always made on the plan of leaving the pendulum free
in the middle of the swing, which, as we have seen, is
the worst construction, especially as the angles were sure to.
be made veiy far wrong, from the difficulty of making them
right on that construction.

54. There is however a certain mechanical difficulty in
the construction of these escapements, which has probably
been a greater obstacle to their use than the supposed
mathematical objection. It will be easily perceived on
looking back to the drawing of the escapement that there
is some risk of the teeth of the scape wheel, when driving
up the slope of the pallet, sending the arm too far by
causing it to rise too quickly ; and if it does, the hook at
the end of the slope will not catch the tooth as it ought to
do, and two or three teeth will slip past at once : this is
called tripping. Various contrivances have been resorted
to to prevent it; the most obvious is to put the slope on
one arm, and the hook on another by the side of it j the
arm with the hook is not allowed to fall so low as to require
raising by the wheel, and so is always ready to receive a
tooth when it is not raised by the pendulum; the pendulum

78 cumming's escapement.

raises both the hook-arm and the pallet-ann together. This
is Cunmung's escapement, with the omission of some halls
which he added by way of giving ' momentum' to the arpis,
in complete ignorance of mathematical principles^ that being
the very thing we ought to avoid as much as possible ; and
with the arms set upon springs instead of turning On
pivots and carrying weights, it is Hardy's escapement^
which the transit clock at the Cambridge Observatory has.
But this is a compUcated arrangement^^nd I believTevea
these stationary hooks (as they may be called in contrast to
the others) sometimes trip from tiie blow of the tooth
against them, unless they are nndercut, or the teeth so
made to fit the hooks that they cannot be disengaged by the
pendulum without causing a slight recoil in the wheel and
a resistance to the pendulum, which is of course very ob-
jectionable, especially as the force required for it will vary
m different states of the clock. It wiU now be seen why
the similar contrivance which I mentioned (45) as having
been appUed to the dead escapement does not answer; for
the separate arms carrying the dead part of the pallets are
liable to these same objections, and moreover on account of
their own weight they affect the pendulum after the manner
of a remontoire escapement without the angles properiy
adjusted.

ME. HLOXAM'S ESCAPEMENT.

55. A form of the gravity escapement has lately been
invented by Mr. Bloxam, the inventor of the dipleidoscope
(9), which when it is so made as to satisfy the proper con-
ditions respecting the angles, (which he had unfortunately

HE. BLOXAH's ESCAFBHENT. 7d

bot discovered until after he had constructed the escape-
ment withoat an; particular regard to tiie angles), seems
likely to possess eret; qnaMcation that is requisite to
produce s perfect escapement, and with no inordinate
difficulty of construction. By Mr. Bloxam's pramission

I ^Te a drawing, and a short description of it, as it
wiU require to be made. A.C, BC are the two arms.

CLOCKS.

carrying flat stops corresponding to the common hooka
at A, B, one of which is represented as stopping a tooth
of the scape wheel at B. I have omitted the pendulum
in the drawing for greater distinctness. The scape wheel
has only nine teel^^ and consequently moves through
20° at each beat, and its motion therefore will take a Ion-
ger time, or will be more gradual, than if it only moved
through &° as usual. Concentric with the scape wheel and
fixed to it are two other wheels of the form called cam
wheels in machinery, though no great accuracy is required
in the form of the teeth for this purpose. These wheels are
so placed that one of the nine teeth or cams of the smaller
wheel is ready to raise the arm B C by means of the pro-
jecting piece E when that arm is left by the pendulum at
its lowest position ; and while the wheel turns through 20**
the small wheel is to raise the arm B C through Si', if the
pendulum swings 2°; and in like manner the larger cam-
wheel raises the other arm through the same angle, by
means of the projecting piece A B.

The reason why two cam-wheels are required, in order
to completely satisfy the condition respecting the angles,
is, that as one arm must be raised by the lower part of the
wheel and the other by the upper, they cannot both be
carried through the same angle, unless the wheel which has
to work the longer arm is larger than the other.

Now the effect of this arrangement is, first, that the
arms are raised with much less friction than when a tooth
slides alonjsc a sloping pallet: secondly, the rise taking a
longer time! there is no risk of the a^s being driven too
far by their own momentum; thirdly^ the pressure of the

MR. bloxam's geavitjt escapement. 81

teeth of the scape-wheel upon the stops is much less than
in a wheel of the uaual number of teethj^ and consequently
the Mction at unlocking is mucKless ; in fact the pressure
is so little that tho stops^ inst^ of being undercut^ may
be sloped a little the other way without the pressure being
sufficient to lift them^ and therefore the £riction at unlocking
may be reduced to nothing. To show how safe from trip-
ping this escapement is, I have seen the weight in Mr.
Bloxam^s clock pulled by hand, and so increased to more
than double of what was required to work the escapement,
without its exhibiting the least tendency to trip. And it
may be observed, that even if the angles should not be
quite correctly adjusted, the causes of error are so much
reduced by the absence of nearly aU friction, that hardly
any variation of the arc can take place: in fact Mr. Bloxam
tells me that he has never been able to detect a variation in
the rate of more than a second a week even in his clock as
now made with the angles of escape not half the proper size.
1 have no doubt it might easily he made on a large scale
with perfect accuracy and no great amount of trouble, and
it might also be combined with a remontoire in the train,
for the purpose of effecting those objects for which a train
remontoire, letting off about every half-minute, is desirable
in tunet clocks, independently of their accuracy of per-
formance, for which see § 172, &c. It may be convenient
to state the proportionate dimensions which I find wiU be
required for the different parts. Suppose we intend the
radius of the scape-wheel, (which is very light, being cut
out of a plate of thin steel) to be 2'5 inches, then we
must make the other parts as follows :—

82 CLOCKS.

Eadius of larger cam-wheel 1"24\

Badius of smaller cam-wheel 1* J supposing the

Distance from centre of wheel > angle a = 120

to axis of arms ... 7*45 \ and c = 84'

Length of arms (to pallets) 7* /
These dimensions will allow -^ inch for the depth of loddng-
if it occupies an angle of 24'^ and iV if i^ occupies as much
as 30': anything between the two will do very well. If the
scape-wheel is half this size everything else must be half
the size. The counterpoises a, 6, are added because I
believe the arms cannot be made light enough to do with-^
out, when they act through an angle of 168'.

56. Other escapements without number have been
invented: indeed there is a story of a celebrated clock-
maker saying he would undertake for a wager to invent
a new one every day. But a description of them would be
of no use in a merely practical treatise, as the escapements
themselves have never come into use. Perhaps the most
ingenious, as well as curious, was Harrison^s, who, when he
was only a carpenter, invented it to save himself the trouble
of having to go so frequently to oil the escapement of a
turret clock, which he had undertaken the care of. It has
no friction on the pallets, but has an immense recoil; and
though a degree of accuracy is attributed to one made by
him, which is evidently fabulous, it is said (which is pro-
bably not fabulous) that nobody else could ever make them
to answer. A description of it may be seen in several of
the Encyclopaedias, and in Beid's ' Treatise on Clock-
making.' We will proceed to consider another matter, which
though appareaily piinute is of great importance.

COMPElfSATION OF PENDULUM.

57. All the substances of which a pendxdum rod can
be made increase in length as their temperature increases.
Let I be the length of the rod, d I its increase for any given
number of degrees of heat, and d t the corresponding increase
of t, the time of the vibration of the pendulum, then (re-
membering that dl \& Y^rj small compared with /, and so
f Y) iJ^y l>e neglected),

—t 77 ^-^u' ^'"^^ Tl- 2

if for shortness we put m for j the rate of expansion of the

material of the rod for some given number of degrees of
heat. And the dailj loss of the clock, which we may call
d T, will be 43,200 m in seconds, whatever is the length
of the pendulum.* The following is a table of the value
of i», or the rate of expansion in length of the following
materiab, for 10° of heat : —

Wyte-deal - - - *000023

Hint glass - - - • 48

Steel rod - - - - • .... 64
Cast iron ... '....GG

Lronrod - - - - '...•7
Brass - - - * • ... 10

Lead -...16

Zinc • . - - •...17

Mercury (in buUc» not length) ' . . 100

* This same calculation will show us how mtich a pendulum ought
to be shortened when it loses, or lengthened when it gains — assuming
the weight of the rod to be immaterial compared with the bob. Sup-
pose for instance, that 33 threads of the screw are contained in an
i&oh, and that the whole length / of the rod is 45 inches ; then each

84 CLOCKS.

Thus for a common pendulum rod of iron wire, we
see that dT for an increase of temperature of only
10^=43200 X -00007=3 sec: or the clock will lose a minute
in three weeks ; and if the pendulum is adjusted to go right
in winter, it will lose about a minute a week in summer. Even
a deal pendulum would vary nearly a third as much as this.^

58. We want therefore some contrivance which wiU
compensate this expansion of the rod; that is, which wiU
always raise the centre of oscillation of the pendulum as
much as the expansion of the rod lets it down. If the rod
had no weight, and the bob were merely a heavy point, this
would be the same thing as saying that the centre of gravity
of the bob must be kept at the same height ; and as the bob
of compensated pendulums always is heavy in proportion to
the rod, this is approximately true, and with the addition of
a small quantity, according to a simple rule, it is sufficiently
correct for practice.

59. The most simple kind of compensated pendulum is
one in which the material of the bob expands so much more

thread, or each complete turn of the nnt, ivill raise the bob by a
quantity = -rjjij-, which we may, as above, call m; and the corres-
ponding daily alteration in the time being = 43,300 m, will be just
30 seconds. Consequently, if the head of the screw is divided, as it
usually is in regulators, into 60 divisions, with a pointer over them
a turn of the screw one division to the right or left will accelerate or
retard the clock half a second a day.

* You must not expect to find this result actually take place in a
common house clock : the other causes of disturbance in such clocks
are so large, that they may either overbalance or aggravate the effects
of heat upon the pendulum rod. I believe they will generally be of
the former kind, since the heat makes the oil more fluid, which
in the common recoil escapement will accelerate the clock.

COMPENSATION OF PENDULUM. 85

than that of the rod^ that a bob of moderate length resting
on the bottom of the rod will raise its own centre of gravity
as much as the expansion of the rod lets it down. A deal
rod^ with a leaden bob about f ths of its lengthy will be thus^
compensated. For the ratio of the expansion of the wood
to that of the lead is we see about -f ; and consequently
a bob whose centre is |th of the length of the rod from its
bottom, will compensate the rod.

60. But we want to know how much longer than the length
of the simple pendidum the rod must be in order to carry a
long enough bob. Let l^ as before, be the simple pendulum,
or (as we assume it to be) the distance from the point of
suspension to the centre of gravity of the bob ; x the addi-
tional length required, or half the length of the bob ; m the
rate of expansion of the rod, n that of the bob. Then
(/+«) m^ the expansion of the rod downwards, must=;i? »,
the expansion of half the bob upwards; ora? = ^7-. This
calculation will make the leaden bob of a 39 inch deal pen-
dulum about 13 inches long, and the rod 45^. It is foimd,
however, on account of the difference between the centre
of gravity and the centre of oscillation, that the proper
length is 14^ inches; and the practical rule may be given,
to add ^th to the length of compensating material deter^
mined by calculation on the hypothesis of the centres of
gravity and oscillation being identical.

61. The principle of the mercurial pendulum is exactly
the same as that of the wood and lead. The rod is of steel,
and the mercury is put in a cast-iron cylinder (in the best
pendulums) screwed to the bottom of the rod. Only it is
to be remembered that the rise of the mercury in the

88 MERCT7BIAL COMPENSATION.

cylinder will be diminished by the lateral expansion of the
cylinder itself^ and consequently a rather greater height
of mercury is required than that given by merely taking
the tabular rate of its expansion. The old form of mercu-
rial pendulum was that of a glass cylinder standing on
a itirrup at the bottom of the rod. The chief advantage of
the iron cylinder is that it can be made of a more regular
shape^ and that it takes the same temperature as the rod^
and communicates it to the mercury more rapidly than the
glass. Captain Kater^ in his chapter on compensated pen-
dulums in 'Lardner's Mechanics' (from which the above
table is taken)^ says he has successfully employed, as a
cheap mercurial pendulum, one made entirely of glass, the
rod and cylinder being blown in one piece. The height of
mercury required in an iron cylinder is stated to be 6'6
inches. The best mercurial pendulums are actually tried
ftnd adjusted for compensation at various temperatures, by
adding or taking away mercury as may be required.

62. But mercurial pendulums are too expensive for
common use, and would cost nearly as much as the dock
itself, for pendulums weighing several cwt.; and wood
is open to the objection that it is liable to twist, and can
never be completely protected from damp, which of course
alters its weight ; and therefore some other kind of metallic
compensation is necessary. Now it will be seen on looking
at the table, that the ratio of the expansion of steel to that
of brass is *61. Consequently, if we can make a pendulum
of steei and brass rods in the proportion of 1 inch of steel
to * 61 of brass, and so arranged that the brass rods carry
the bob up while the steel ones let it down, it will be com-

GRIDIRON COMPENSATION PENDULUM. 87

pensated. The only convenient way of doing this, is to
make the brass rods (for there must evidently be a pair
of them^ one on each side of the main rod) rest on a
nut at the bottom of the main steel rod^ and hang ano-
ther pair of steel rods from the top of the brass ones
to carry the bob at their lower end. Therefore the one
length of brass has to compensate two lengths of steel ; and
since the compensating rods must not reach above the
point of suspension of the pendulum, it will be evident
tiiat this cannot be done with only one pair of compen-
sating rods ; and in fact it can only just be done with two
pairs; for suppose the brass rods to be quite as long as the
main steel rods, or all the rods to be of the length /, we
must have iln the expansion of the brass rods upwards
= Slm the expansion of the steel rods downwards;
and since — = -61, this is only just possible; and if iron
is used instead of steel, it is not possible, since the ratio of
the expansion of iron and brass is *7, which is more
than 7. And therefore a completely compensated gridiron
pendulum of steel and brass requires nine bars (as the com-
|)ensating rods must go in two pairs), and one of iron and
brass could not be made with less than thirteen bars. Grid-
iron pendulums have now been superseded by those which
I shall next describe.

63. The greats expansion of zinc than brass obviates the
necessity for so many bars, the ratio of iron and zinc ex-
pansion being only '41 ; and a very good and elegant and
tolerably cheap compensated pendulum can be made of iron
and zinc rods ; or, what is the more simple and common form
of it, a zinc tube may be made to rest on the regulating nut

88 ZINC COMPENSATION.

at the bottom of the main rod, and this zinc tube carries an
iron tube fastened to it at the top, and carrying thq bob at the
bottom. In compensation by rods it is necessary to add
more than ^ to the length of zinc aad brass given by the
calculation in § 60, because the difference between the cen-
tre of gravity of the bob and the centre of oscillation of
t)ie pendulum is greater where there are compensating rods
or tubes of considerable weight, than where the compensa-
tion is contained in the bob : in other words, the bob ha^
to be lower to produce a pendulum equivalent to the re*
quired simple pendulum when the rod is heavy than when
it is light. I find that for a l^sec. pendulum (88 inches),
for which the zinc compensation, if the centres of gravity
and oscillation were identical, would be 61*6 inches, it is
necessary to add nearly i to complete the compensation,
taking into account the weight of the rod and tubes, the bob.
being a cast iron cylinder a foot long; and the total lengtk
of the pendulum, from the top of the spring to the bottom,
of the bob, requires to be nearly 97 inches instead of 88.

64. There is another kind of compensation, a compound
of both the former kinds, which was invented by Smeaton^
and was generally used by Holmes, a celebrated clockmaker
of the last century. The rod is of glass, and it carries on
a collar at the bottom a zinc tube about 12^ inches long,
from which is hung an iron tube, which carries a lead
cylindrical bob of the same length as the tubes themselves,^
and enclosing them, so that the pendulum looks as if it
had merely a glass and lead compensation. I wonder it is
not more frequently made now that glass is cheap, as it
requires no polishing as a zinc and steel pendulum does.

COMPENSATION FOR SPRING, 89

or is thought to do^ and I suppose it is equally effective.
It is evident that the expansion of the zinc and half the
length of the lead upwards has to compensate that of the
glass and iron downwards.

65. In all cases a little additional compensation is re-
quired on account of the variation in the strength of the pen-
dulum springs which diminishes as its temperature iucreases.
The amount of it depends upon the stiffiiess of the spring
with reference to the weight of the bob and the length of the
pendulum, and can only be ascertained by trial. According
to some experiments published by Mr. Dent, the compen-
sation of the spring requires about ^th to be added to the
ordinary compensation of the steel rod in a seconds pendulum
of the usual weight; and consequently about half must be
added to the compensation required for a wooden rod. I
am told that in a short pendulum the compensation re-
quired for the spring was a great deal more than \ of that
required for the steel rod; and indeed it is evident that this
must be the case, for the elasticity of the spring must pro-
duce less effect upon the rate of a long pendulum than a
short one of the same weight; and therefore in a 14 or even
an 8 feet pendulum the compensation required for the spring
must be very little indeed compared with that of the rod.

66. It is evidently a considerable advantage of a mer-
curial compensation that it affords the means of actually
tiying the pendulum and adjusting it so as to compensate
accurately both the variation of the strength of the spring
and the expansion of the rod at any two extremes of heat,
by merely diminishing or increasing the quantity of mer-
cury ; which cannot be done without a good deal of trouble

90 MERCURIAL BULB COMPJfiNSATlON^

in a pendulum made of solid metals. With the view of
obtaining a cheaper mercurial compensation than that of a
cylinder full of that metal I have suggested the following
method^ which as far as I know is new. Make a koUow
cast iron ball with a short neck in which a piston fits very
accurately. It is evident that if the ball is neariiy fiUed
with mercury and the piston can be made to fit mercury,
tight, the expansion of the mercury will raise the piston
through a height which depends upon the ratio of the
thickness of the piston to the quantity of mercury which
the ball will contain. Consequently if the ball is fixed to
the bottom of the pendulum rod by a thing like a pump
sucker, and the piston is made to carry the bob resting on
a short cross bar, this apparatus may be used to compensate
the pendulum, and will require only a small quantity id
mercury. And as the depth of the piston in the ball does
not signify, the quantity of mercury can be varied at
pleasure ; or it may be altered by putting bits of iron into
the ball in the place of so much mercury. The only diffi-
culty is to make the piston mercury-tight. Mr. Dent has
succeeded in doing this for a 39 inch pendulum, even with
such a heavy bob as 70 lbs. I doubt however whether it
would be safe to use this plan where the mercury is con-
stantly under such a heavy pressure as that ; but perhaps it
may answer for pendulums of twice the weight of those
which are usually put to astronomical clocks at present,
and of which the mercury alone costs £4 or £5.

67. There are two other kinds of compensated pendu->
lums which have this peculiarity, that tRey do not depend
upon the difference of the rates of expansion of their nm^

LEVER C0MP1N8AT10N. 91

terials. The first of tiiem, the lever compensatioii, vas it
seems tried Itj Graham, the inventor of the dead escape-
ment, bnt abandoned by him for the very superior merca-
lial compensation ; and was afterwards completed by EUicott.
I have lately seen it nsed in some small Pr^ch clocks, and
fLerefore it may be worth describing.

AG is the main rod of iron,
B D a lever resting on a fulcrum at
C fix«d to &ie bottom of the rod.
(There is anoth^. lever, exactly
the same, only set the opposite
way, which is with a portion of i
the rod on the left hand omitted
in the drawing for greater clear-
ness). Aba strong collar fixed to
the main rod anywhere near the
top. Between this collar and the
^ort end of each lever ib put a
bar, either of brass or iron, and
tlie bob is supported by pins or
rollers D resting on the long ends
of the two levers. Now if the

ratio of the long arm to the short arm of each lever is the
name as that of the funonnt of expansion of the rod AB to
that of the main rod, it is evident that the bob will be kept
in the same place. Theoretically A may be anywhov, and
AB may be either of iron or of brass; but the less ex-
pansion AB has the shorter must be the short arm of the
lever, which is objectionable for several obvious reasons.
A more serious objection to the pendulum altogether is

9^ CLOCKS.

that/ on account of the Mction at D, which ia sliding
friction of a bad kind, the bob was found to move by
jumps, and moreover the compensating rods must be very
thick to avoid bending. It has indeed been proposed to
remedy this by supporting the greater part of the weight of
the bob on a spring, and leaving only just enough weight,
0^ the levers to ke)e|i ti^m to their bearing; but it is com-
plicated enough lihr^iidljf, and can have no advantage over the
n^ore simple zim ^OHipensation, until the laws of nature
are altered, mi itt W&isia expand equally.

68. Tiiid otW kbd of homogeneous compensation is,
I think, but foir one. practical difficulty, much more pro-
mising ; for if this difficulty can be got over, it would
afford the means of compensating a pendulum 50 feet long
and a ton in weight, with as little trouble and expense
as a small one, as well as a very convenient method of ma-
king the finer adjustments for time, without stopping the
pendulum. If the pendulum spring, instead of bendiog
^m a fixed poiat, is passed through a sUt ui a fixed cock,
and is itself carried by another cock above, which admits of
being raised as much as the pendulum increases in length,
the effective length of the pendulum will evidently remain
the same. Therefore if the upper cock is made to slide in
a vertical grove and rests upon an upright bar of the same
material and length as the pendulum, standing on a firm
support at the bottom, the expansion of this bar upwards
will exactly compensate the expansion of the pendulum rod
downwards. And in favour of this method it is said that
if the bar and the pendulum rod are taken from the same,
piece, we are sure that their rate of expansion will be the

B0MOOEII2OTI8 COMPETE SATION.

same, whereas no two experiments witK different pieces of
the same metal ^ve exactly the same result. But as this
rod acts by poshing, not by pulling, it would have to be
very thick to support the cock for a long and a heavy pen-
dolnm without bending.

69. The sune object might however be effected in ano-
ther way and with sevoral incidental advantages, provided
the objection I shall mention can be removed. I«t tiie
pendulum be hung from a fixed cock A as usual, only a few
inches higher, and with tlie spring reaching a few inches
above the end of the pallet arbor. B C D is a cast iron
lever with its pi-
vots at C turning
in two Vs in a
strong cock firmly
fixed to the wall.
At one end D is
fixed a wire or rod
SEFof the same
Ifaigth and mate-
rial as the pendu-
lum rod, A squa-
red portion of this
rod passes through
the cock E to keep
it from twisting,
and ends in ascrew
passing throng
another coekF, and
has a nut G below.

91 CLOCKS.

E and F would be cast all in one piece and fixed to the wall*
The other end B of the lever at the same distance as D is from G

is so made as to clip the pendulum spring, but not so tightly
that it cannot slide under a moderate pressure ; and in order
to produce this pressure and keep the lever steady, a weight
W is hung on to that end of the lever. Then as the pen-
dulum rod lengthens, the compensating rod lengthens too,
and lets the weight W pull down the end B of the lever,
and so makes the effective length of the pendulum the same
as before. As the motion would not have to be quite -^ of
an inch to compensate a 14 feet pendulum for 40^ of heat, it is
not of the least <»nsequence that the end of the lever moves
in a circular arc and not in a straight line; and the longer the
pendulum is the longer the lever should be in order to dimin*
ish the curvature of the arc which its end has to describe. .
The practical objection to this kind of compensation, to
which I referred, is, that any alteration in the length of the
spring is found to affect the rate of the pendulum, not uni-
formly, but in some variable way which is not reducible to any
fixed law. This is entiidy an experimental question, and I
have no means of knowing to what extent this variation takes
place, or whether any experiment exactly similar to this has
been tried. I do not suppose that this compensation would
be equal to the others; but considering the advantages of long
and heavy compensated pendulums over short or uncompen-
sated ones, tEai the impossibility of compensating very long
pendulums at a moderate expense by any of the usual methods,
I should be inclined to try it where the building affords &cil-
ities for a pendulum as long as 21 feet (2^ sec), such as there
is in Doncaster Church, with however ft very inferior dock.

SHAPE OF PENDULUM BOB. 95

quite iinfit for tke work it has to do. I may add that when
the tower shakes under the ringing of the bells^ as all
towers that have not spires on them do with a heavy peal of
bells^ a long and heavy pendulum is especially necessary.*

70. There are a few other matters relating to pendulums
which may as well be mentioned here. First as to their
shape. Until lately pendulum bobs^ except mercurial ones^
were almost universally of the shape of a common magnifyr
ing glass or lens, and such pendulums are therefore called
lenticular. This sliape was adopted on account of its pas-
sing through the air with less resistance than any other
figure that could conveniently be used. But they are liable
to this objection : if one of these bobs were set on a rod
with its broad side instead of its edge towards the directioDi
of motion, the pendulimi would vibiiate in a different time
(independently of the resistance of the air), because the
moment of inertia of a circular plate turning round an axis
placed anywhere at right angles to its plane is greater than
if the same axis were placed in the plane. Consequently if
the pendulum rod should from any cause get so placed or
twisted that the lenticular bob (which, approaches to a f^t
plate) does not always vibrate with its largest or central
circle in the plane of motion of the pendulum rod, the time

* I take thb oppoTtanity of correcting a mistake in Southey's
well-known book called The Doctor, wherein he laments over the re-
moval of the old peal of bells in Doncaster Church on account of the
inability of the tower to bear them any longer. The old peal mr^
removed in 1835, but only to be recast, the two largest beUs being
cracked ; and the new peal was put up in the same year, and is one
of the heaviest peals of eight in the kingdom, the tenor weighing
S2cwt.

96 CLOCKS.

bf vibration will vary; and in nearly every common clock
the bob of the pendulmn may be observed to have that kind
of twisting motion which is familiarly termed. wMUng, es-
pecially when it swings a large arc.

But this twist of the bob can produce no effect upon
the time of vibration, if the bob is a cylinder or any other
solid of revolution having the rod of the pendulum for its
axis. And the pendulum is also less likely to acquire that
motion, if the bob is such a solid of revolution, than if it
presents a surface unequally exposed to the resistance of the
air, as the lenticular bob does if it is ever so little twisted.
A sphere (which Holmes put by Smeaton's advice to the
Greenwich Hospital clock) is iaconvenient, not only because
of its requiring so much width for the pendulum to swing
in, but because a slight error in making the hole for the rod,
which throws it out of the axis of the sphere, causes a
greater disproportion between the mass on each side of the
rod than in a longish cylinder or a prolate spheriod having
the rod for its axis. Therefore upon the whole a cylinder
is probably the best shape for the bob ; and there is no
objection to its top being made a portion of a sphere, when
the bob is made of cast iron, as it rather improves the ap-
pearance, and also prevents anything from settling upon the
top, as sometimes happens in church clocks, with bits of
mortar and the like, the effect of which we shall see pre-
sently. The pendulum of the clock in the frontispiece is
of this shape. It may be convenient to state that a casrt
iron cylinder 9 inches wide and 12 inches high, with a
spherical'top rising 2 inches more, and a hole 2 inches wide
all through it for the compensation tubes, weighs 2 cwt.

REGULATIOl^ OP PENDULUM. 97

within a very few pounds ; and the centre of gravity of the
bob is about 7i inches from the top.

71. The next point is the regulation of the p^dulum*
The common and well-known method is to raise the bob
by a screw at the bottom of the rod when the dock loses^
and to lower it when it gains ; and the quantity by which
this must be done for any given bss or gain of the dock
may be determined approximatdy in the manner stated in
the note at page 83« But it is difficult to do this without
stopping, or least disturbing the pendulum, which requires
the dock to be set again ; and therefore two other methods
are used for making the finer adjustments in regulators and
in turret clocks with heavy pendulums, which require a strong
and coarse thread to the screw, and must be hdd steady while
the screw is turned to avoid twisting the pendulum spring.
One is, to have a small weight sliding on the rod and kept
in its place by a spring collar, which allows it to be moved
up and down by a blow with a small hammer; raising it
accderates the pendulum, only in a much smaller de-
gree than raising the. heavy bob, and therefore it admits
of greater accuracy, The other method is to have a few
small weights to lay on the top of .the bob ; adding th^n
of course raises the centre of gravity, and of oscillation,
and accelerates the pendulum; if they were put si the
bottom of the bob they would produce the contrary effect.
When the bob has a round top the little weights may be set
on spikes (of whi^h there should be a pair, one on each side
of the rod)/ or in a cup, or on a ring on the top of the bob.

The amount of accderation produced by any given

small weight put on the top o! the bob, will evidently vary

98 CLOCKS.

with the length of the hoh directly (that is with the height
above the centre of gravity or oscillation at which the little
weight is placed), and the length of the rod, and the weight
of the bob, iwvenely. Let / as before be the length from
the top of the pendnlnm to the c.g.iA the bob (assuming it
as before to be identical with the centre of oscillation), h
the distance of the e.g. of the bob from its top, M the
weight of the bob, m the little weight to be added, and dl
the qnantily that the e.g^ is raised thereby; then it is
easily proved that ^^=::^~r- = — ^if wepntr for — • And
as in § 57, the corresponding daily acceleration d'L will
= 7-TTw itt seconds. Suppose, for example, that -j = -^
(as if / is 88 inches, a 1^ second pendulum, and b^=1\ in.),
M = 2 cwt., andfl» = lib.; then^^T = jg§^= 16 sec;
or an ounce weight put on the bob of such a pendulum
would accelerate it just one second a day. The pendulum
of the Exchange clock, a 2 seconds pendulum with a bob 20
inches long and weighing above 3 cwt., was regulated sojne
time ago by putting a penny on it.

We may now leave the pendulum and escapement,
which may be considered the mathematical parts of a clock,
and return to the consideration of the merely mechanical
parts.

HAEBISOFS GOING BAEREL.

72. The general construction of the going or time«
keeping part has been explained already (18). But for
docks that are to keep accurate time, there is yet something
wanting, viz., a contrivance to keep them going while they

HAEE1B0N B GOING BARREL.

are bemg wound np, for that of conise takes the action
of the weight off the dock, and so the scape-wheel will not
escape nnlesa some equivalent piessnre ia sppUed to the tiain.
In common house-clocks and the cheapest watches there is no
Buch contriTance, and they stand still while they are wind-
ing np ; bat in all others the apparatus which is applied for
the purpose is that invented by Harrison, and called the
ffoitif barrel, or rtdehett, in we^t clocks, uid the ff<mg
fiuee in watches and spring clocks. This drawing shows
the arrangement of
it. The barrel with
its ratchett and
click are the se
as before
plained; bnt the
dick c is not now
placedon the great
wheel, but upon
. another whed rid-
ing on the arbor
of the barrel be-
tween the great
whed and the barrd ratchett : this whed has also ratchett
teeth cot upon it, but turned the opposite way to the barrel
latdiett, as shown at B, and the dick EC bdonging to it is
s long arm turning on a pivot C in the dock-&ame ; and
this second ratchett whed is connected with the great wheel
in any convenient way by a spring S S, having oiLe end Sxed
OD the ratdiett wheel, and the other end pressing against a
pta on the great wheeL The action is this : while the
7 2

100 CLOCKS^

dock is going, the weight polls the barrel and both
ratchetts to the left, and the going ratchett, by means of
the spring S S, presses the great wheel in the same direO'
tion ; and as the clock goes on, one tooth after another
of the ratchett R slips nnder the long dick, and this cansea
the drop wUch may be heard about every five minut(»
in regolators and in good watches. When the weight
is taken off the barrel by winding up, the going ratchett
immediately flies back a Uttle towards the right, but is
stopped as soon as one of the teeth arrives at the cUck, and
there it is held ; the spring continues to press the great
wheel as before, with nearly as much force as when the
weight is acting, and so keeps the wheel in motion for this
short time that the clock is winding up.

DIAL WOEK.

73. The only thing that remains to be described in the.
going part of clocks is the dial work, or the machinery by
which the hands are moved. The minute hand is set upon
the square end of a socket or pipe, which fits rather tightly
ou the long projecting arbor of the centre wheel. It must
not be quite tight, or the hand could not be put forward or
backward when the clock wants altering ; and the requisite
degree of tightness or friction is obtained as follows.
The pipe on which the hand is set is about an inch long,
and has a whed fixed to its other end (the use of which will
be described in the next section, and which may be called
the hour<-whed), and the pipe slides on to the arbor pretty
easily ; but before it is put on, a slightly bent oval spring,
nearly as bug as the diameter of the whed, with a squife

DIAL WOEK. 101

hole in thie middle/ is dipped on to tlie arbpr with the
concave side outwards^ and the square hole fitting on
to a corresponding square, cut for about ^th of an
inch on the arbor, so that .the spring is always car-
ried round with the arbor; then the pipe is put on, and
the wheel rests against the concave ^eof the spring ; then
(omitting the hour-hand for the present) the hand is put
on, and generally a small cap or collar in front of it; the
collar is pushed back so as to force the wheel more tightly
against the spring, and a pin is, put through the end of the
arbor just in front of the collar. It is evident, therefore,
that the hand and its pipe will be kept steady on the arbor
by the pressure between, the collar and the spring, and the
friction of the spring upon the hour wheel, but that it can
be turned when necessary. Sometimes the hole in the
spring is left round instead of square because it is less trou-
ble, but it is a slovenly practice, and it requires much more
pressure to produce the same degree of steadiness when the
friction of the spring acts upon the small diameter of the arbor
than when it acts upon the large diameter of the hour wheel,
74^ Besides carrying its own hand, the long hand pipe,
and the wheel belonging to it, have to turn the short hand,
and also in striking clocks to let off the striking part. The
form of hour-hand which was formerly used in regulators is
this : the minute-hand socket has a pinion on it, and this
pinion works a large .wheel with twelve times as many teeth
as the pinion, which therefore turns round once in twelve
hours ; this wheel has the twelve hours engraved upon it, and
there is a hole in the dial though which the figures appear,
and a stationary hand or index pointing to the proper figure.

102 CLOCKS.

This might have been done in a still more simple way>
and without incuiring the friction of that wheel and pinion,
by setting the hour drde on the arbor, of the great wheel,
which turns in twelve hours. It is of no consequence that
it would be turned with the arbor in winding up, because
you would only have to stop winding at a place which would
leave the proper figure of the hour circle under the index.

These moveable hour circles are now abandoned^ on
account of the small figures moving past a hole being so
much less easy to see than a hand moving in the usual way.
The now obsolete day-of-the-month wheels, which required
setting for five months in the year, showed themselves
through a hole in the same way. But if a hand were
merely put in the place of the moveable dial, it would turn
the wrong way, that is the opposite way to the other hand |
and therefore an intermediate wheel is now put betwe^ the
pinion of the minute-hand socket and the hour-hand wheel,
and the multiplier 12 (when there is no striking) may be
divided between these three wheels and their pinions as we
please ; and in regulators the hour-hand usually points to a
separate dial, or set of figures engraved on the lower part of
the large dial, and corresponding to the small dial for the
seconds-hand on the upper part.

There is another way, which is sometimes adopted, of
working the short hand on a separate dial, and without the
intervention of this second wheel, viz., by putting the hand
upon an axis which goes through the frame of the clock,
and carries a wheel working into another equal wheel fixed
on to the great wheel, which turns in twelve hours. The
great wheel itself is so large that it would be inconvenient

DIAL WOEK. 108

to have another of the same size working into it, and thii
is the reason of this other wheel being fixed to it. There
is so much less Motion in this way of working the hour
hand directly from the great wheel than by going up to the
centre wheel and then down again by two more wheeb, that
I wonder it is not more commonly adopted. The only
objection to it is that if the hands want setting they must
be set separately; but a regulator dock requires so little
alteration that the hour hand never has to be meddled with
unless the dock has been allowed to stop.

75. AH these methods howeyer are different from that
which must be used when both the hands turn on an axis
in the middle of the dial, as they do in all clocks ezcept
astronomical ones, and sometimes in them. In that case
there is a wheel of the same size as the whed we have
called the hour whed placed by the side of it and driven
by it, and therefore turning the toronff way once in an hour,
and having on its arbor a pinion with six or more leaves :
this whed may be called the reverse hour wheeL Its
pinion drives a whed with twdve times as many teeth,
which is fixed to a socket or pipe riding on the former one ;
and this pipe carries the hour hand, and will evidently turn
in the rigit direction once in twdve hours. This hour
hand pipe is not indeed really carried by the minute hand
one ; for in order to take the wdght of it off the centre
whed arbor, it rides upon another fixed socket or pipe sur-
rounding the minute hand pipe and set upon a cock which
extends over the minute hand whed and is screwed to the
frame: this fixed cock and pipe are called ^ cannon^ So
that the apparent central axis of the hands of a common

104 CLOCKS.

dock oonaiflts, first, of the centre wheel arbor; seeondljr',
of the pipe to which the long hand is fixed; thirdly, of the
cannon; and fourthly, of the hour hand pipe; and, fifthly^
if there is an alarum to the clock, of the pipe to which the
little alarum dial is. fixed* This arrang^n^t of the dial
woik is the.most cinmsy part of Eng^h and French dbdcs.
It is done better in the American; and I shall propose
what I think a stQl better arrangement ofit, in §87, in con<^
nexion with another alteration of the usual construction of
eight-day docks.. Occasionally the seconds hand is also
set upon a thin arbor within all the others and traveb
round the large dial, instead of having a small one to
itaelf ; this is a very bad practice on account of the in*
creased friction, which it causes, and such docks are rarely
made now.

EQUATION CLOCKS.

76. The thingiit called Equation Clocks bdong to the
subject of dial work; for they are (or rather were) docks
for showings but not going, true instead of mean solar
time; which was done by communicating a secondary or
superimposed motion to the hands, so as to advance or
retard them according to the equation of time for every
day in the year, lliey were never in common use in
Bngland, though they have occasionally been made as
curiosities; but Mr. Yulliamy says in his pamphlet before
quoted, that until December, 1826, 'all the French public
docks of any repute were made to show solar time.' The
machinery by which it was done was, as may be supposed^
complicated; and as it is perfectly useless, and worse, than

MONTH AND YEAR CLOCKS. 105

useless^ and a description of it may be found in Said's
Treatise on €loekmaking and other books^ I shall not
describe it. For house clocks there appears to have been
a somewhat more simple method of doing it^ by making the
dial itself revolve slowly^ according to the equation of time^
while the hands went uniformly in the usual way. The
dial would have to turn about half round between November
and February, the figure XII appearing nearly at the usual
place of IX in November, and at III in February, with
other smaUer oscillations in t}ie remaining nine months.
And after all the ingenuity thrown away upon these con-^
trivances, true time could not be shown by any of them as
accurately as by a common clock, with an equation table
such as that printed at page 11. For the equational motion
was, in all the plans, communicated to the dial or dial work
by means of a plate of an irregular oval form set upon a
wheel revolving in a year; the form of the plate was such
that the radii, from the axis on which it turned to the
edge of the plate, were proportionate to the quantity by
which the clock ought to be before or behind the sun; and
tiie plate as it revolved pushed some moving frame work
jEEurtber from the centre or nearer according to the time of
year* And it is evident that no great accuracy could be ob-r
tained in this way except upon an inconveniently large scale^

MONTH AND YEAE CLOCKS.

77. Occasionally clocks are made to go for a month or

even a year. This is done merely by the addition of one

wheel or two below the usual great wheel, and increasing

the weight to four or forty-six times as much as usual,

p a

106 CLOCKS.

Occasionally two barrels are naeA, to avoid the great straiii
upon the teeth of one great wheel and the adjacent pinion.
One string is then sometimes made to mn off both baiteb
together^ carrying one weight between the two lines ; which
however has a pulley for the string to pass through to
keep its tension equals though the pulley has no sensible
motion. The barrels will of course turn half as many
times round in the month w year as if one end of eadi
string was fixed to the frame in the usual way^ and the one
weight was divided into two. Chronometers are also made
to go long periods in a similar way^ by the use of two or
more main-springs to drive one wheels as tins secures
greater uniformity of force than one very strong spring*

THIETT-HOUE CLOCKS.

78. These clocks are seldom made now as English or
French house clocks. Most of the Dutch and many of the
American clocks however are so. When a thirty-hour
clock winds up with a key like other clocks, in order that
it may have only three wheels in the train, the minute
hand arbor does not belong to a wheel in the tnun, but to
a supernumerary wheel, which is driven by the great wheel
in the same way as in one of the methods I described for
working the hour hand' of an astronomical clock, and the
great wheel turns in two or three hours. In the Dutch
clocks and the old English thirty-hour clocks, the arbor
of the great wheel is not used to wind up by, but comes
through the frame and carries a wheel which works the
hour and minute hand wheels both together, being smaller
than one and largw than the other : or some equivalent

HUTQBNS'S ENDLESS CHAIN. 107

anangemeot, of which many vadetiee mi^ be conoeived.
Fot as the arbor of the great wheel is used to cany tliiB
dial working wheel, it evidently canuot be used also to
wind up the barrel; uid accordii^ly instead of a barrel
there is used a sort of dee^ pulley with spikes in it to
prevfait the rope or chain from slipping : this pulley is not
fixed to the aibor but lidea upon it, and it is connected
with the great wheel by a ratchett and click as bef(»e des-
cribed* One end of the rope carries the clock weight loid
the other end a little w«i^t merely to keep the rope steady
and to take hold of to paU up the great weight by when
you wind np the clock.

7 9. There is however another way of appl^ug this sort of
spiked pnlley, which
deserves noticeon bc-
conntof itsprodudng
the cnrioos effect of
keqiing the weight
sdingupoa the dock,
at the same time that
it is being wound up.
Itis called the endlett
eioM of Hnygens.
P is the spiked pulley
fixed on to the great
whed Bibor, not now
by a ratehett and
click but rigidly ; p
anoDierspikedpuUey
whichmay rideeil^

108 CLOCKS.

•on the same axis or on any other conveniently placed, and
having a latchett and a cUck fixed to the clock frame. The
midless chain abed passes over both pnlleys, and in the
loop formed by c^ on the right side of both pnlleys it car-
ries the weight W hnng by a common pulley; a little
counterbalancing weight to is hung to the other loop ab ;
this little weight is somelames merely a large ring hung on
to the chain. Now if the string b is pulled down by hand
it will puU up c and so raise the weight W, which being
hung by a moveable pulley will nevertheless still press upon
the string d and so keep the elock in motion by pressing
on the right side of the principal pulley P. If the clock
ha3 a striking part, p may be the pulley of the great wheel
of that part, the click behig fixed to that wheel; and then
the clock may be wound up at any time when it is not
striking. Only in that case it must be remembered that
rWght wiU descend in half the time that it descend, in
when the pulley p never has any motion to the right, or
the click is fixed to the frame ; and the same will be the
case with only a going part, if the cUck is fixed to the
great wheel instead of to the clock &ame, for then both
puUeys will turn together ; but while the clock is being
wound up only half the weight will then act upon the great

wheel.

SPEING CLOCKS.

80. There is yet another kind of elock, which difiers
from all that I have yet described in having for its main-
taining power not a weight but a long spiral spring, which
is coiled up in a box or barrel as tightly as possible when
it is wound up, but with room to uncoil itself for a few

8PRIKG CLOCKS, 109

toms of the bairelj in doing which it moves the train
which is connected with the barrel just as a weight does.
The simplest constroctioii^ which is used in all the French
clocks and watches^ is this : the great wheel is fixed to the
barrel that contains the spring; the outer end of the spring
being fastened to the barrel^ and the inner end to a strong
arbor which goes through the barrel, turning in the caps of
the barrel, and ends in the winding square, and also carries
a ratchett wheel, of which the click is fixed to the dock
frame, to hold it as you wind up. And therefore this
kind of clock requires no maintaining power to keep it
going while winding up; for the tension of the spring is
acting upon the barrel at that time as much as any other,
in fact rather more. But on the other hand the force of
the sprinff is much crreater when it has been just wound
up, tJaTwhen it is^ly run down; with however this
lemarkable, and apparently anomalons exception j that it is
found that there is a certain position of the spring in
which its force is nearly the same for three or four turns,
but no more. Consequently, as a watch only requires a
few turns to wind it up for a day, the variation in force in
!French watches is slight, compared with that in the clocks
which go a week or a fortnight, and in which the spring
has many more turns to make than in a watch* This is
one reason of the inferiority of French watches, and still more
80 of clocks^ to English ones, both in price and quality. .

81. For this inequality of force is removed in English

spring clocks and watches by the use of what is called the

fmee. The fasee is nearly a cone, that is to say, a cone

whose slant side is concave instead of straight, with a spiral

110 CLOCKS.

groove cut round it from one end to. the other, as on the
barrel of a weight-dock, for a string or chain to ran in*
The spring is enclosed in a barrel as before, but the barrel
does not carry a wheel, and its arbor, instead of being used
to wind up by, has a ratchett and click merdj for the
purpose of adjusting the tension of the spring. A catgut
cord, or a chain, is wound round the barrel, and the loose
end of it fastened to the thick end of the fusee. The fosee
is fixed upon the winding arbor, and has the great wheel
riding upon it with a ratchett, just as the great wheel of a
weight-clock rides on the barrel arbor ; and the best clocks
and watches have a 'going ratchett' also. As the fus^ is
wound up, it draws the cord off the barrel along the groove
until it is all wound off the spring barrel on to the fusee*
And it is evident that when the tension of the spring is
greatest, it is pulling at the thin end of the fusee, and when
the tension is least it puUs at the thick end ; and therefore,
if the radius of the fusee is made to decrease, as the force of
the sprii^ at the corresponding point of winding up in^
creases, the force communicated to the great wheel will be
constant.

S2,, In order to prevent the cord from being broken by
over-winding, there i3 a kind of lever fixed to the frame;^
with a hook to it, so placed that as the cord advances to*
wards the thin end of the fusee, it pushes this lever aside,
so. that its hook catches hold of a long tooth projecting from
the end or cap of the fosee, and stops it from being, wound
up any farther. As the cord recedes agaia, the lever is
allowed to recede under the pressure of a small spring behind
it, and by the time the fusee has made one revolution^ the

SFBIN6 CLOCKS. Ill

lever and its hook have got oat of the vay of t]ie long
tooth.

83. Ftobabljr few readers of this book require to be told
what the chain of a watch or a spring clock is like, bat it is
proper to describe it in a ' radimentar^ treatise.' It coa-
msta, then, not of links set across each other, bat of pistes,
alternately' one and two, rivetted together; bat the hole in
the single plates is bo large that the rivet does not stick
tightly ia it. I

Here are two I
pairs of links,!
drawn on a scale I
wEiich the reader I

will think more St for a drawing of the chains of a suspen-
sion bridge than of a watch or even a clock. A. chain of
this kind never twists, but will only bend in a plane (co-
nearly so) parallel to the plates of which it is composed.

84, These clocks are most freqnently made to stand on
a bracket, and alwa^ of snch a size that their pendnlnms
can only be abont 10 or 18 inches long; and as their bobs
are small also, we know what the resalt most be as regards
their accaracy. However, when they are well made, with a
fosee, and not exposed to a temperature which freezes the oil
(whic^ is much above the freezing point of water), they will
go nearly as well as a coarsely made long clock of the old
fiishioned kind. Sometimes they require a good deal of
trouble to set them so as to beat equally, for if they are not
■0 set, they are very likely to stop, as they have g^ierally,
and the foreign ones always, very httle force to spare. This
position is not, as is conmumly suj^sed, that of actual ver-

112 CLOCKS,

iicalitj, but merdj of verticalitj relatively to the escape-
ment ; they ought indeed to coincide^ but they frequently do
not; and oraisequently after the bracket has been made
quite level, it is found either that the crutch wants bending^
or the clock raising on one side by bits of card. They are
much more likely to stand steady, and also easier to adjust,
if the two hind feet are taken off, and one put instead in the
middle between where they were.

85, These are now almost the only. English clocks
(except regulators) that find any sale; and even these are
getting fast superseded by the better class of American
clocks, and by l^nch ornamental clocks, neither of which,
however, will last nearly so long. With the latter it is no
doubt quite hopeless for us to compete, as, besides the
greater cheapness of their labour, the French appear to pos-
sess what I may call a smaller eye and finger than English
workmen, and they are able to perform delicate and oma*
mental work with much greater quickness and facility. And
as those who chiefly regard the beauty of the figure of their
clocks seldom care much about their entrails, they consider it
of no consequence that a good English clock is better for the
natural object of a clock than a foreign one. Whether it
would be possible to mcmufactwre clocks on a large scale as
cheap as the American ones, I am not able to judge. I have
been told that, but for the cases, it would. But unless the
English dockmakers take some steps towards either altering
the kind of docks that they make, or can fiind out some
cheaper mode of making them, there is no doubt that there
wiU soon be no house clocks, except regulators, made in
this country. The old-fashioned, fiiU-length house clock i^

THREE-QUARTBR liEKGTH CLOCK. 118

now nearly exploded^ on account of its ugliness^ size, and
deamess, as compared with the American clocks, which go
Bofficientlj well for ordinary purchasers.

No one who has seen the inside of an American clock
€an help seeing that onrs are unnecessarily heavy, and waste
a great deal of the force in merely overcoming their own
inertia and friction. An American clock goes a week with
both the weight and the fall for it not half of what they ai6
in the common English clocks ; and as a large pendulum
requires no more force to keep it going than a small one, it
is evident that about fths of the moving power in our
clocks is wasted. (The commendation of the American
docks cannot be extended to the fixing of their pendulums,
which is as bad as possible.) I have also seen some very neat
French clocks, about the same size as the American, but
much more highly finished, and with dead escapements,
going a week with a very small weight.

86. A clock might be made very much better than
any English spring dock, or any of the foreign ones, and
quite as cheaply as the old long clock, and at least equal to
it in performance and very superior in appearance, and
therefore more likely to sell, by making the case only of the
length required for a seconds pendulum. This may be done
in three ways : 1. By hanging the weights by three strings
instead of two : the lower pulley should be let into the
weight instead of occupying the height of 3 or 4 inches
above it, and should be as broad as the space between the
weights will allow. I have converted an old long clock
into one of 'three-quarter length' in this way, and cut off
the large and ugly and useless pedestal of the case. The

114 CLOCKS.

second method is to iftake the barrel ids of the usual diame-
ter; and the third and best is to make the number of teeth
in the great wheel half as many again. Or the second and
third methods may be combined in any convenient propor-
tion. In all these cases of course the weight will have to
be half as large again, except that, as I said before, it in
now unnecessarily heavy, because the wheels are so. I may
observe also that the third of the above methods will re-
quire a barrel of only |ds of the usual length, and therefore
all the arbors and the space between the plates may be so
much less. Mr. Dent now makes nearly all his regulators
■*^ in this way, and such clocks take up no more room, except
in length, than a common spring clock; and for all the
reasons I have mentioned I beg to suggest' the adoption oi
this size of clock to both the makers and the purchasers of
clocks : the faces should be about the same size as those of
common spring clocks ; one door serves for the body and
face, or the whole of the front and sides take off at once.

87. And with this alteration I think there may very

well be combined that alteration of the dial work which I

referred to in § 75, as it will also help the arrangement of

making the barrel to turn only 11 times instead of 16 in

8 days. Those who are acquainted with the American

clocks will see that this plan is partly borrowed from them.

The arrangement will be pretty clear from this drawing.

The scape wheel and second wheel will be worked by the

centre or 90 minute wheel as usual, which may have 70

teeth driving a pinion of 7 on the second wheel with 54

teeth driving the scape wheel pinion of 6. I adopt these

small numbers on the supposition that all these driven

NEW BIAL WORE.

pinions are to be lantern pinioiu, as tliey are in tbe Ame.
rican clocks, which is one of the reasons of their going
with such small weights, as will be explained in § 126 'on
the teeth of wheels.' The pinion of 8 on the left side of
drawing, not being driven, but driving the 11 horn wheel
of 64 teeth, is not to be a lantern pinion bat a common
one, only hollow, as it is fixed to the wheel of 46 which
rides on the centre wheel arbor and tuns with it in an honr
and an half, and admits of being moved on the arbor when
yon alter the hands, being held by the pin and the bent
spring shown in the drawing, as before described in ^ 73.

CLOCKS.

The advantages of this phin are, fiwt that the ftiction
of the large and heavy 12 .hour wheel pipe riding on the
' cannon ' is got rid of, or rather that pipe ia reduced in
size so that it need not be any larger than the usual hour
wheel pipe; secondly, the minute hand pipe is got rid of
entirdy, and consequently the weight and friction of that
arbor is also reduced ; thirdly, the 12 hour wheel ia driven
directly by the tram instead of in the usual roundabout
way ; fourthly, the discharging pin is put on the hour wheel
itself instead of on the usual reversed hour wheel, and con-
sequently it must always agree with the hand ; whereas at
present clocks are not unfrequently put together so as to
strike when the hand is nearly a minute from the proper
place : thie hour hand can also be adjusted by simply pulling
its pipe forward when the minute hand is off, as there is
room to slide tiie 12 hour whed out of gear with 4he pinion
that drives it. The hour arbor is to be kept in its place by
a small collar at its end, over which there stands a cock
which may be screwed on from the outside of the clock
framie. . The lifting piece of the striking part will have to
be inside the frame; but that, as any clockmaker will see is
of no consequence, as it will only require a pin to go
through the hole in the front plate to lift the click of the
repeating work, instead of going through from the front to
the inside to stop the pin wheel as usual. In the striking
part the reduction of the turns of the barrel from 16 to 11
may be made (besides the methods above described for the
going part) by increasing the pins and teeth of the striking
wheel in the proportion of 8 to 10 and giving the great
wheel 93 teeth instead of 78, And I have no doubt that

STRIKING PAET. 117

if a Spiral spring is put to the hammer, as I shal! describe
presently, and the higher wheels made aa light as the
American clock wheels, the present size of clock weight
would atiU be quit« sufficient in the striking as well as the
going part. However I shall leave this to the consideratioQ
of clockmakers and proceed to describe the

8TBIKING PAST OP CLOCKS.
88. A clock may be made to etnke one at every honr
without any separate striking part, fay merely putting a pin

118 CLOCKS.

into either of the wheels of the dial work that tarns in an
hour, and a hammer tail or lever over it^ so that the pin
will begin to raise the hammer aboat a quarter before the
honr^ and jnst slip from under it when the minute hand
points to the hour. Instead of the pin there may be put
upon the front of the wheel what is called a mail^ which is
a flat piece of metal cut into a spiral form, as shown in the
drawing ; the efiect of which is that the work of raising
the lever is distributed over the whole hour instead of
having all to be done in a quarter of an hour, but with con-
siderable friction. I have drawn the bammer as worked by
a spiral spnng, instead of the usual long and stiff spring,
which produces a great pressure on the pivot^ and is no
better than the inside bit of a broken watch spring in any
respect, and not so cheap to make and fix. The arbor
should be made thicker than usual at the place where the
spring is put on. This apparatus will require an addition
of about one-sixth to the clock weight, as there are 12 blows
to be struck in the 12 hours instead of 78, and the striking
and going weight are usually about equal. Clocks of this kind
are put in some of the C!ourts of Law at Westminster, and are
just as good for a room as those that strike the number of
the hours, since they call attention to the fact of the hour
being up, and any body who does not know what the hour
must be has only to look. They can of course be made
cheaper than full striking clocks, which require a separate
train of wheels, and which are made as follows.

On one of these wheels are placed any convenient num-
ber of pins so as to raise the hammer tail in succession.
In eight-day clocks the pins are put upon the wh^ next

STRIKING PART. 119

to the great wheels and are 8 or in coarse clocks 6 ; and
the pinion liaving as many leaves as pins^ the great wheel will
turn in the 12 hours if it has 78 teeth^ or one for every hlow
struck in 12 hours. In thirty-hour clocks the pins are set
upon the great wheel. Above the wheel which has the strik-
ing pins there are usually two others^ the highest of which
drives a fan or fly to regulate the velocity of the train : a
pendulum and escapement have been proposed for the same
purpose^ but the fly is perfectly sufficient. One of these two
wheels has another office to perform besides driving the
fly. The one above the striking wheel must turn exactly
round for one or more blows of the hammer. I shall as-
sume it to be once for every blow as it usually is.

89. The principle of all the various ways of letting off
the striking part wiU be seen from the next drawing. A pin
P in one of the higher wheels of the traia^ called the pin
wheels rests against a stop S on a lever^ called the lifHn^
piece, when the clock is not striking. This liftiug piece
turns on a pivot and has a tail^ which is raised by a pin R
or a snail on one of the hour wheels of the going part when
the dock is within a few minutes of striking^ and this lets
the pin P slip past the stop S on the lifting piece; but it is
' not allowed to go far, being presently detained by another
^ stop T either on the same lifting piece or on another con-
; neoted *ith it; the noise made by this is caUed giving
varmn^. When the tune is come for striking^ the pin R
I slips from under the lifting piece and lets it drop^ and so
f the pin wheel can turn round until the pin P has come to 8
* again. But before that happens provision is made for getting
8 out g[ the way if the clock has to strike more than one.

This is done as follows : there is a large wheel called the
loclamg^late or cotint-wieel, which tams in ] 2 hours, and
may therdore conyeniently be put upon the great wheel.
The rim of this locking-plate is marked out into 78 divi-
sions, and then deep notches are cut in it at the BUcoessiTe
distances of 1, 2,8, &c., of the divisions, up to li,iiewot
which are shown in the drawing. The lifting piece has ano-
ther arm which reaches as &r as the locking-plate and has a
tooth which just fits into the notches, Now while the first
blow of any how is striking and the pin wheel is makii^

STRIKING PART. 121

one turn, the locking-plate is turning also in the direction
shown in the drawing ; and in so doing the notch lifts the
tooth of the lifting piece out and makes it rest on the rim
until another notch has arrived for it to fall into ; and the
depth of the notches is such that the lifting piece is moved
far enough to lift both the stops S and T quite out of the
way of the pin P by the time it has gone once round, and
they remain there until the clock has struck the proper
number and the tooth of the lifting piece drops into the
next notch in the locking-plate : which is in fact an hour
dial if the notches are marked with the hours, as the num-
ber under the lifting-piece is always the last number the
dock has struck.

Between twelve and two o^clock it will be seen on looking
at a locking-plate there is one long cut instead of two nicks,
as I have shown in the drawing, because the clock will strike
one blow without having the lifting-piece lifted at all, except
as the going part lifts it. And in like manner in the French
spring clocks which are often made to strike one at the hall'
hour, the count- wheel or locking-plate is divided into 90 parts
instead of 7 8, and all the nicks are made as long as the one
o'clock nick in clocks that do not strike the half hour.

Sometimes instead of a nick for every hour there is a pin
with a slant side, which when the clock has struck the pro-
per number raises the lever to catch the pin P in one of the
higher wheels ; when warning is given the lever is raised by
the going part a little higher to let the pin P clear the first
stop S and stop at the second T, and when it is completely let
off the lever drops and the count- wheel moves on and lets it
fall low enough to clear both pins. This of course is exactly

122 CLOCKS.

the same in principle. The objection to the count-wheel
method of striking is that if the clock is either caused to
strike when it ought not^ or the striking part is allowed to
run down^ or the clock put back past an hour^ it will strike
wrong the next time^ and cannot be set right again without
striking it round till it comes right ; and even this is not
what every body knows how to do ; and it may be useful to
those who have foreign clocks to be told that if you put
your finger behind the clock or into the left side of it and
lift up the only moveable thing you can fed, you can hardly
fa3 to make it strike. There are several other modes of
applying the locking-plate construction, which are occa*
sionally used in turret clocks, but these are much the most
common.

REPEATING STRIKING MOVEMENT.

90. The pl^ which has long been in use in all English
house clocks allows the striking of any hour to be repeated
as often as you please, or the clock to be stopped or put back
past the hour,"^ or made silent, or to be run down, and
still it will strike right as soon as it is made to strike again.
Instead of a complete count-wheel or locking-plate there is
only a portion of wheel L M, called the rack, turning on a

* Borne docks will be found to offer a resistanoe to bdmg put
back past the hour : if they do it cannot be helped ; but the lifting
piece ought to have had its end twisted so that the pin on the reversed
hour wheel.can pass the wrong way by pushing it aside. If a dock
is put hack between warning and striking it will strike : this does not
si^iify in an English dock ; but it will make any of the foreign
docks, which all have the locking-plate movement, strike wrong, and
therefore must not be done.

REPEATING STRIKING MOVEHKNT.

centre 0, and having 13 or 14 ratchett shaped teeth on it.
Another ndios ON of this fr^mentof avheelhas a pinN
•et upon it; and on a wheel called the ttarieheel, which'
will be described presently and tnnu in 12 hours, there is
fixed a gradoated mail with 12 steps in it, such that when
the honr hand points to 6 for instance the pin N can Call
s^amst the 5th step in the snail to such a depth that the
la^ can fiA through the space of S of the teetL Ihe

124 CLOCKS.

rack has a click D E, set on a stud at D, which will hold the
teeth in any given place, a spring G pressing the rack to-
wards the left hand. The arm D E of the click is prolonged
to E, and there rests upon the lifting piece, which is the
same as before, and has a stop T projecting backwards
tlirough a wide hole in the clock frame, and so placed that
when the lifting piece is down in its ordinary position, the
pin P in the third wheel of the striking train can clear the
stop T, but when it is raised it will stop the pin and con-
sequently the train. When the clock gives warning, the
pin R in the reversed hour wheel raises the lifting piece as
before, which lifts the click, which lets the rack fall back
as far as the snail allows it to go.

Over the rack there is a sort of hook K, which is in
fact a pinion with one tooth, set upon the projecting arbor
of the second wheel, {Le. the one above the striking wheel),
and at every revolution of that wheel, and therefore at
every stroke of the hammer, it takes up the teeth of the
rack one after another, and it is therefore called the
gathering piece or pallet. When the clock is to strike, the
lifting piece is let fall, which sets the pin P at liberty, and
also lets the click fall on to the rack so as to be ready to
catch the teeth and hold them as the gathering pallet
gathers them up. After the pallet has taken up the last
tooth, its tail, which is on the opposite side to the hook,
falls upon a pin S at the end of the rack, and is thereby
stopped from turning any farther, which of course stops
the train.

91. If the clock is to be capable of repeating the last
"hour struck when required, the click FED is prolonged

REPEATING STRIKING WORK. 125

backwards and has a string put to it which comes through
the clock case, and when it is pulled the clock will strike.
But if the string is let go too quickly the click will catch
the rack before it has fallen far enough, and the clock will
strike too few ; and if it is not let go quickly enough the
cUck will not catch the rack at the first stroke, and it will
strike too many. Therefore the string ought to be put to
the lifting piece, instead of the cKck, which can be done
just as easily, though I have never seen it so done. If you
find on pulling the string that the clock won^t strike, it is
between warning and striking, and if you leave it alone it
will strike of itself in a few minutes.

92. The star wheel, of . which the construction is
evident from the drawing, is turned ^^ih round at some
time in every hour (it should be done before the work of
the lifting begins, that the clock may not have too much
to do at once) by means of a pin Q, on the hour wheel
catching one of its rays. The pin does not indeed carry
it through the whole distance it has to move, for by the
time it has got about half way the ray at X in the drawing
will have reached the angle of the thing called the Jumper,
sliding up its left hand inclined plane, and as soon as the
point of the ray passes the angle, the jumper, being pressed
upon by a spring, will do the rest of the work and drive
the ray still farther forward by means of the right hand
inclined plane. The jumper also acts as a click to keep
the star wheel steady; a common click would not do,
because it would not allow you to put the clock back,
whereas this one will allow the rays to pass up either of
the inclined planes. In the commoner kind of clocks this

1*^ CIX>OKS.

star-wheel is dispensed with^ and the snail is set npon the
twelve hour wheel (in which case it most be reversed) ;
indeed the only use of the star-wheel is to relieve that large
twelve hour wheel arbor or pipe of the additional weight
of the snail; and if that pipe were reduced to a moderate
me and the twelve hour wheel driveu directly by the train,
as described in § 87^ the weight of the snail might be dis-
regarded.

93. Some clocks are so made that by turning a little
hand which is placed above the dial the clock can either be
made to remain silent, or be allowed to strike. This hand is
so connected with the lifting piece that when it is turned to
' silent' it pulls the lifting piece out of the way of the pin
in the hour wheel by drawing its arbor forward, the pivots
being made long enough for that purpose; and when
turned to ' strike' it pushes the arbor back again. Some-
times the striking is prevented by bringing a stop of some
kind close up behind the pin S or some other pin set upon
the rack, which prevents it from falling when the cUck is
lifted, and so the gathering pallet cannot get past the stop
S. This way is more simple than the other, but the other
has this advantage that the clock can be made ordinarily
silent, and yet it wiU strike whenever the above-mentioned
string is pulled.

I have seen a third way used, viz : the train stopped by
a hook or pin .pushed into the way of the fly. This is a
most blundering way of doing it ; for, as it does not prevent
the rack from falling, the clock is almost certain to stop
between 12 and 1 o'clock, from not having force enough
to drive the deep step in the snail past the. pin N in the

BEIili. 127

rack tail, even if it is made with a bevelled edge for the
purpose. In fact the clock in which I saw it had so
stopped, and I was told it had frequently stopped before^
nobody knew why, I reKeved it from the dif&culiy in
fature by taking away the ' silent' stop altogether. In a
dock with the locking-plate movement however, this plan
would answer perfectly, and is more simj^le than any other ;
and probably the maker of this dock had borrowed the
plan from an old locking plate clock, not recollecting the
difference.

94. It is merdy a matter of taste whether a clock is
made to strike on a bell, or on one of the spird sted
springs of a very deep note that have lately come into use*
Perhaps in a room the spring has a more agreeable sound;
but they are not heard so far as a bell, and at a distance
they have a thin sound, very unlike what they pretend to
imitate, a heavy church bell ; and therefore for a clock to
stand in a hall and strike for the whole house, a bdl is
certaroly the best.

QUAETEBS.

95. House clocks are occasionally made to strike quar-
ters. The machinery for that purpose is the same as for
striking the hours, if we suppose two hammers to be put
in the place of one, and an additiond set of pins on the
striking wheel to raise them. If they are what are called
dmg^dong quarters, on two bells, this wheel may be made
exactly like the hour striking whed, only with two sets of
pins set on its opposite sides so as to raise the two hammers
dtematdy. But if there are four or more bells, the rim of

128 CLOCKS.

the striking wheel is spread out so as to form a cAime barrel,
with pins sticking out of it like the barrel of a musical
box, and these pins raise the hammers successively, which
are all set on one axis. I may here remind clockmaters
(as I have found it necessary to do so before) that though
the repeating movement may be used for the quarters as
well as the hour,, when the second, third, and fourth quar-
ters are only the first quarter so many times repeated, yet
when the tunes or changes are different the locking plate
ought to be used ; for if the repeating plan is used and
one quarter gets struck wrong or stopped, it throws the
whole of the^tunes into confusion, the clock playing at tha
next quarter the right number of changes, but the wrong-
order, that is, a piece of the tune of one quarter, and a
piece of another ; whereas if the locking plate is used the
right tunes will always accompany the right number of
changes, and any person will hear directly not only that
they are wrong, but how they are wrong, and that they
merely want striking by hand once or more to bring them
right, which it is much more difficult for an unskilful per-
son to ascertain when the tunes are wrong but the number
right. The work for connecting the repeating quarter
movement with the hour striking part is also more com-
plicated than that of the locking plate, which is remarkably
simple. But as quarters are so much more rarely put to
house clocks than to turret clocks, I shall reserve the des-
cription of the mode of connecting them with the other
parts of the clock, as well as some other matters belonging
to them, for the chapter on church clocks.

96. Small spring clocks are occasionally made to strike

QUARTERS. 129

the quarters only when they are wanted, as in the night,
and to strike them after striking the preceding hour, just
lis repeating watches do. In this case, the repeating part
is not wound up periodically as in a common clock which
strikes quarters ; but by pulling a string or pushing in the
handle of the watch, you wind up a barrel containing a
main-spring, which, when you let it go again, works the
3triking movement in the usual way, according to the
position given to the rack or locking-plate by the wheels of
the going train. Bepeating watches are rarely, if ever,
made in England, or at least by English workmen ; and
from the quantity of work that has to be put in a small
compass they seldom go very weU. Eor this purpose a
small clock is much better; and such clocks are usually now
made portable, that is with a balance instead of a pendulum,
and go by the name of carnage clocks y and consequently
they possess the advantage of being secure against the dis-
turbances of housemaids. I shall have to mention them
again in the next chapter.

ALARUMS.

97. If you take the pendulum off a clock with a recoil
escapement, you will hear it beat about as quickly as the bell
is struck in an alarum ; and the striking there takes place in
the same way as if a double hammer were put on the end of the
crutch of a recoil escapement, just long enough for one end
of the hammer to reach the inside of a bell at one extremity
of the beat, and the other end at the other extremity. The
manner of letting it off I shall describe presently; but

130 CLOCKS.

first it may be asked by aa observant person, how it
happens that such a small weight as that of an alarum, fail-
ing only a few inches> able to strike such a vast number
of blows, when the striking part requires a' weight of 10
or 12 lbs. to strike so few as it does. The reason is this :
the common striking weight has to raise the hammer against
a strong spring; and the force with which it strikes the
bell depends upon the force of that spring, and the distance
it is bent ; but in an alarum, the hammer is merely thrown
from side to side by the action of the alarum weight, which
has consequently nothing to overcome but the friction; and
the velocity of the strikiug depends upon the proportion
between the moment of inertia of the hammer and the
momentum (or product of the weight and the fall) of the
alarum weight. An attempt appears to have been made to
produce a common striking part on this principle, but with-
out success, because in that way it cannot strike with both
force enough and slowness enough to be distinct.

98. But an alarum is wanted to let off, not always at
the same time, but at an arbitrary time. Por this purpose,
all we have to do is to make the letting-off pin moveable on
the wheel which carries it. If the common lettiug-off pin
were made moveable upon the hour-wheel, we might make the
clock strike when the long hand is at 50 m. instead of 60 m.
And in like manner, if we put a letting-off pin for the alarum
on a cap, or key^ which fits tightly on to the socket of the
12 -hour wheel, we can make it let off with as much accuracy
as is required at any portion of the twelve hours we please.
This key, which carries the pin, has its socket prolonged
forward, so as to carry a small dial or hour circle under the

ALARUMS. 131

hour hand^ which always travels round with it; but the key
does not fit so tightly that it cannot be moved by the hand
so as to make a pointer in the hour hand point to any time
we like on the alarum dial; and then it wiU let off at the
time so indicated. There is no occasion for any stopping
apparatus beyond a single lifting piece^ and a pin in the
striking barrel^ which rests against the stop on the lifting
piece when it is not raised high enough to let the alarum
go. The string of the weight is attached to a wheel
exactly like a recoil scape- wheel, either of the crown wheel
or the plain kind, and when it is let off it runs till it is
down. Of course it must not be wound up until within
twelve hours of the time when it is intended to strike.

THE WATCHMAN'S CLOCK.

99, This is mentioned incidentally in the parliamentary
papers respecting the great clock for the new Palace, as
being the invention of Mr. Whitehurst, of Derby. It is
otherwise called the teU-tale clock, its object being to watch
watchmen; whose tendency to sleep, like other men, in the
night, had caused buildings protected by them to be con-
sidered less secure than those which axe only protected by
the ordinary precautions of mankind before they go to bed.
In the watchman's clock there are pins sticking out round
the dial, one for every quarter of an hour; and the duty of
the watchman, in order to testify his own vigilance, is to go
to the clock every quarter of an hour, and push in the
proper pin, which only admits of being so treated for a few
minutes : consequently, if in the morning any pin is found

132 CLOCKS.

sticking out, it indicates that the watchman was absent, in
body or mind, at the corresponding time. There is a clock
of this kind, on an improved plan, lately put up in one of
the lobbies of the House of Commons. The face and pins
are not open but inclosed behind a glass, and there is a
handle at a convenient place outside the clock case, which
communicates with a small lever standing over a part of the
circle in which the pins move ; and as the pins are carried
round in a sort of a moveable dial, it is evident that pulling
the handle when any particular pin is under the lever, it
may be easily made to push that pin in, and can do so at no
other time. In fact, if the lever ended in a pencil, and the
moveable dial carried a rim of paper set round the figures,
puUing the handle would make a mark upon the paper,
showing exactly the time at which it was done. But the
paper would want renewing continually, and the pins do
not, but are made to pass over an inclined plane at their
back in another part of their journey (performed after
the hour of inspection), and so to push themselves out
again: for this purpose it is most convenient to make
the revolving dial to contain 24 hours, so that there may be
time enough in the morning to examine the pins before
they are replaced by the inclined plane.

ELECTRICAL CLOCKS.

100. If the pallets of a clock, instead of being worked
by a pendulum, are attracted by pieces of soft iron, magnet-
ized alternately by means of an electrical communication
with the pallets of another clock, as they move to each side,
or with the teeth of the scape-wheel successively, the two

ELECTRICAL CLOCKS. 138

clocks will evidently go exactly together. Not only this,
but if you take oflf the weight as well as the pendulum, and
move^e pallets of a recoil escapement backwards and for-
.they will drive the scape-wheel instead of letting
3^/ escape, only they will move it, and consequently the
hands, the wrong way; and, therefore, if the scape-wheel
and pallets are reversed, they will drive the hands the right
way. Instead of two magnets, one is sufficient, if the
pallets are drawn one way by a small weight or a spring,
and the other way by the magnet. This is the ordinary
form of what are called electrical clocks.

101. But still further, the whole train of the clock may
be dispensed with, except the dial wheels, by making the com-
munication take place at longer intervals, such as every half
minute. The wheel of the minute hand would then require
60 ratchett-shaped teeth, and a pair of large pallets to
be put over it in the same way as the recoil pallets over
a common scape- wheel ; and at each beat the wheel would
move through the space of half a tooth. A click should in
any case be added to secure the wheel from slipping back at
the moment of escape. The advantage of a minute-hand
moving a visible space at intervals, such as half a minute,
will be pointed out under the head of 'turret-clock re-
montoires,' § 172.

102. Another way in which this may be done, is to let
the dial work be driven by a weight or spring, wound up
just like a common clock, and make the electricity let it off
instead of driving it. This method is peculiarly adapted to
clocks with large faces and heavy hands ; for in this way a
dial, or any number of dials, of any size might be worked by

184 CLOCKS.

au escapement and train no larger than that of a common
astronomical dock. The only objection to it is the difficulty
of keeping a galvanic electrical machine in perfect action^ so
that you can depend upon a beat never missing ; for it not
oidy requires some attention to the galvanic trough^ but a
small particle of dirt on the rim of the wheel, which is
divided into conducting and non-conducting spaces, some-
times interferes with the contact. Mr. Dent had an electri-
cal dial, of the first construction just now described, going
for some time in his shop, but he found it required constant
attention to prevent it failing in this way.

103. When, on the other hand, a large and strong clock
is employed to drive a number of other clocks, magnetic elec-
tricity may be used, the large clock by its own force pulling
or rather sliding a strong permanent magnet out of contact
with its armature at the proper intervals. Mr. Dent also
kept a dial of this kind going for some time, making a small
turret-clock movement work the magnet; and this experiment
answered perfectly. Of course the clock which has to do this
extra work should have some provision to prevent the inequa-
lities of force produced by it from reaching the pendulum.
It will be seen how this is to be done when we consider the
subject of turret-clock remontoires. This general explanation
of electrical clocks may be interesting to those who have read
in the parliamentary papers on the subject, that it is pro-
posed to have an electrical communication between the great
clock at Westminster and the Observatory at Greenwich,
and perhaps also to make it work the small clocks in vari-
ous parts of the building.

104. Now that the very convenient practice of setting

ELECTRICAL CLOCKS. 135

all the clocks in the kingdom to Greenwich instead of local
time is becoming, general^ it would be by no means an use-
less employment of the electric telegraph to send the exact
time at a certain hour every day or every week to all the
telegraph stations on the various Unes of railway. The whole
kingdom would thus have the advantage of an indication of
the time as perfect as that afforded by the ball on the top of
the Observatory at Greenwich, which is dropped every day
exactly at one o'clock. Whereas at present, the time can
only be obtained in places where there is not a good meri-
dian instrument by the tradition of travellers or railway
guards, which is equivalent to saying that it cannot be
obtained at all with accuracy. 1 have sometimes found
a difference of five minutes between the time of the public
clocks in large towns less than 100 miles apart, and not ad-
mitting of the excuse that it was the difference of local time,
because, unfortunately, it has been occasionally the wrong
way, i. e. the clock in the west has been faster than the
clock in the east.

MUSICAL CLOCKS AND CHIMES.

105. These are merely common clocks, which let off a
musical box, or a small organ driven by a weight, or a chime
barrel in a church, in the same way as an ordinary striking
part. A chime barrel is exactly the same as the barrel I
before mentioned for playing a tune at the quarters, only
much longer, having to play a longer tune and on at
least eight bells, to each of which there are generally two
hammers, because when a note has to be repeated quickly,
one hammer could not fall and rise again quickly enough.

136 CLOCKS,

A musical box is the same in principle, only the music is in
the springs raised by the pins on the chime barrel, instead
of those springs being levers working hammers that strike
on bells; and accordingly musical boxes are generally re-
paired by watchmakers. Organs involve other considera-
tions besides those of clockmaking, though many of the
German clockmakers repair these clock organs; indeed
they are hardly ever applied except to German clocks.

Clocks are occasionally made to perform other feats,
which I do not consider as properly belonging to the art of
horology, but merely toys; and it is true of clocks, as
of human beings, that if they profess to do a great many
things, they seldom do them well. This remark, of course,
does not apply to church clocks with chimes, which are on
a large scale, and can have ample power and space to do
the additional work.

TEETH OP WHEELS.

106. The theory of wheel-cutting does not belong more
to clock-work than to any other machinery in which wheels
are used, and it is too large a subject to enter into fully
here. But it may be useful to make a few general remarks
upon it, and I must refer the reader to other works, such as
'Camus on the Teeth of Wheels,' ^Willis's Principles of
Machinery,' &c., for the geometrical investigations by which
these results are obtained.

First, it is evident that the more teeth any two wheeli
have which are to work together, the less friction there will
be, and the less it will signify whether the teeth are acca-

TEETH OP WHEELS. IST'

lately cut of the right shape. For if the teeth were infinite

in number, and therefore infinitely small, there would be

no sliding friction at all, and the wheels would merely roll

upon each other; and on the other hand, the fewer the

teeth of each wheel are, the farther they have to slide along

the teeth of the other wheel. And as the same proportion

must be kept between the wheels and pinions of a clock

train, whatever the actual numbers are, the number of teeth

or leaves in the pinions is at once an indication of the

degree of labour which has been expended on that portion

of the clock. In the best astronomical clocks no pinion

has less than twelve leaves,** and sometimes as many as^

sixteen. In the striking part of clocks, there is no need of

the same high numbers, because the uniformity, or amount

of the force of the train, is of no great consequence (within

reasonable limits) so long as it is always sufficient to raise

the hammer.

107. Another thing to be remarked in clock-work is,
that the pinions are all driven by the wheels, except the
pinion of the dial- work which drives the 12-hour wheel,
and the pinion which drives the locking-plate when it is not
placed upon the great wheel of the striking part ; whereas
in machinery for raising heavy weights, the pinions gene-
rally drive the wheels. And this is of consequence for the
following reason. When two wheels act together, the teeth
which are in contact may happen to be either entirely on
one side of the line which joins the centres of the two
wheels, or on the other, or on both sides. If the teeth have
passed that line before they come into contact, the action is
said to be after or behind the line of centres; ^ndivice vend.

138

In this figwe, D,C, represent two

te^Ii of the driving wheel, and d, e,

two corresponding teethof the driveB

wheeL Now, althoogh the; are here

represented as inclined to each other

at the same angle iu each ca«e, ;et

any one mnst see at once that the

friction between C sad e, after the

line of centres, is very moch less than

between D and d, before the line of

centres : no degree of friction (short

of adhesive friction) conld prevent G from driving e, if force

enongh is applied to it ; whereas if the point of contact

of D and if is a good way &om the line of centres, and the

Bor&ce of D rough, a great force applied to the driving whed

might merely drive the point of the tooth d into the side of

the tooth D. The difference between drawing a walling*

stick along the ground after yon and pushing it before you

is an tllnstratiou of the difference between friction after the

line of centres and before ; and a very moderate degree of

roughness will make it impossible to pnsh it if it makes a

large angle with the ground. It is evident therefore that

machinery will go much more easily when the teeth of the

wheeb are so arranged that all the wheels are driven behind

the respective lines of centres. Now it may be shown

geometrically, that with teeth of the common form a wheel

cannot drive a pinion with leaves of sensible thickness witii-

oat any friction before the line of centres, if the pinion has

less than eleven leaves. This, therrfore, is another reason

for using no pinions iu delicate clocks with leaa than twelve

LANTERN PINIONS. 189

leaves, eleven being an inconvenient number, and of course
the higher the number the better.

108. There is, however, a kind (rf pinion^ in which
(when driven, but just the opposite when driping, for which
therefoie they are unfit) the action will always be after the
line of centres, however few its leaves may be : it is a pinion
in which the leaves, instead of being radial or of the leaf-
shape, are round pins set in a ring round the axis; and
from their appearance, these are called lantern or b(w jnmans.
I have drawn the pinion of the scape- wheel in p. 79 as a
lantern pinion. Of course, in these as in all other pinions,
there will be less friction with many leaves than with few;
but whatever friction there is will be entirely of the more
harmless kind. The Dutch clocks always have these pinions,
which are merely bits of wire stuck into wooden arbors, and
«^ i. U» »«n wh, fl«, «U go «.h « ««o™.. of «
that would completely stop a clock with the common
pinions, and their pinions are the last thing in the dock
to wear out. The Erench have also long used them in
their turret-clocks, and it is stated in one of the parlia-
mentary papers, by Mr. Dent, that they have been found to
show no signs of wearing after sixty years: whereas in
clocks made wholly with teeth, if not very accurately made,
the pinions and the wheels that work them will be found to
have worn themselves out of shape in a few years. I have
seen a report made by a man who was sent to examine a
turret-clock, made by a London maker, only fourteen years
old, in which he stated that he found the pinions had
been already twice shifted to get a new bearing for the
teeth, and that they were now thoroughly worn out. Of

i*0 CLOCKS,

coarse this was an extreme case ; bat it would not have
happened with lantern pinions and equally ill-cut teeth,
because they would only have had the more moderate fric-
tion of the action after the line of centres.
• 109. Another great advantage of these pinions is, thai
there is considerable risk of spoiling solid pinions, espe-
cially large ones, in hardening them. I have seen a large
pinion with half the leaves flown completely off in harden-
ing ; and of course the risk of this adds to the expense of
those that are sound, and also very often causes them not
to be hardened at all, which is just one of those things for
which you can have no security except the character of the
maker. Whereas the lantern or box pinions never break,
and are made merely by driving hard steel wire pins into
the holes in the box, which are bored with great quickness
and accuracy by a sliding drill and a dividing engine. Con-
sequently, besides their other advantages, these pinions are
probably, and when they are of large size, certainly, cheaper
than solid steel pinions, which require cutting, hardening,
and polishing, and often break when they are done.

It must be remembered by those who are not used
to them, that lantern pinions require the teeth that drive
them to be cut of a different shape from teeth that drive
common leaves, the teeth that drive the common leaves being
epicycloids traced by a circle of >4a^*the radius of the pinion
rolling upon the driving wheel ; while the teeth to drive
pins are epicycloids traced by a circle of the same size as the
pinion itself. No doubt very few teeth, especially in small
clocks, are really epicycloidal, but some portion of circular
arcs pretty nearly coinciding for a short distance with an

LANTERN PINIONS. 141

epicycloid ; and where the teeth are numerous, and there-
fore small, there is very little difference. But wheii the
teeth are large, the difference is sensible, and there seems no
reason why the cutters of the teeth of large wheels should
not be made of the proper shape more frequently than they
^e. It ought, moreover, to be remarked that, whether the
teeth are circular or epicycloidal, the practice of topping, or
turning off the tops of the teeth by way of correcting the
depths is entirely wrong, because it takes off the most curved
part of the teeth. If the teeth are cut right, and the depth
is found to be wrong, the centres are wrongly placed, and
should be altered, not the teeth, which are innocent.

110. It is not indeed quite true that the action of a lantern
pinion begins when the acting side, but when the centre of
each pin, is on the line of centres ; and therefore the action
is not so completely after the line of centres as a leaved
pinion of twelve or more teeth. But practically this is no
objection to their use ; first, because none but the most ex-
pensive clocks have pinions of twelve, and it is not in clocks
of that kind that there is much to be gained (as regards fric-
tion) by using these pinions ; and secondly, the advantages
of easy construction wouM still remaiQ on the side of the
lantern pinions, especially when they are large. The scape-
wheel of the Exchange clock is made in this way, although
the pins are leaf-shaped, because it has twenty of them, and
is therefore so large that it was found impossible to harden
a solid pinion properly. For the same reason Mr. Vulliamy
makes his large pinions of gun-metal, as hard as it can safely
be used, which however is much softer than hard steel, or
even cast iron. Thirdly, when you come to pinions of high

142 CLOCKS.

numbers, the angle corresponding to half the thickness of
the pin is so small, that it is of no consequence whether the
action begins that anall distance before the line of centres,
or exactly at the line, for the nearer jou come to that line^
the less friction any deviation from it produces ; and there-
fore making the pins of the Exchange scape- wheel of the
leaf-shape instead of round was quite an unnecessary and
very expensive refinement ; and Mr. Dent now makes all
the pinions of the going trains of his turret-clocks lantern
pinions, with round and hard steel wire pins, and the ease
and smoothness of their motion is remarkable, even in
a case where it was necessary to use a pinion as low as seven,
which will be described in § 177.

END OF CHAPTER I.

143

Chapter II.
ON WATCHES AND CH^LONOMETEES.

111. I have already said that the only mechanical dif-
ference between a watch and a dock^ is that a watch will
go in any position^ but a clock only in one ; for although
timepieces in cases like small bracket-clocks^ only with
a balance instead of a pendulum^ are popularly called
docks^ they are really watches^ differing only from common
watches in tiieir size, and in the balance being set horizon*
tal, or in a plane perpendicular to the planes of the rest of
the wheels. Such clocks have of course the advantage of
being portable, and* are called carriage clocks. But imless
they have compensated balances, they are mudi more affected
by changes of temperature than pendulum clocks, or watches,
which are kept at a pretty uniform temperature by being
earned in the pocket, as will be explained in § 124.

112. If you take a common spring dock, with its
wheds and escapement arranged exactly like that of which
a drawing was given at p. 49, and instead iA the crutch for
the pendulum put a whed of the nature of a fly-whed, this
will be v»y nearly a watch. Not quite, however; for it still
differs from a watch in this, that the fly-whed ot balance has
no spring, and so its vibrations wiU depend only upon its:

144 WATCHES AND CHRONOMETERS.

own moment of inertia, and the. force of the train. And
this last dependence is just what we want to get rid of, or
to compensate in such a way that comparatively large vibra-
tions of the balance shall be performed in the same time as
smaller ones. Dr. Hooke ascertained, among his numerous
other discoveries and inventions, that the vibrations of a
spring in large or small arcs are very nearly isochronous.
The reason of which is that the force with wliich a spring
endeavours to resume its position generally varies as the
angle through which it is bent, with the exception before
mentioned in § 80 ; and a body acted upon by such a force
as this (as a pendulum moving in a cycloid is) must oscil-
late through any distance in the same time. Consequently
if one end of a spiral spring is fixed to the frame in which
the balance-arbor turns, and the other to the balance itself,
in such a position that when the spring is at rest the pallets
stand half way between each beat, and the balance is set in
motion, it will go on vibrating in very nearly the same time,
whether the force of the escapement drives it through a
small arc or a large one. In fact, with pallets of this kind
the watch will set itself going, because a tooth of the scape-
wheel must always be pushing against one or other of the
pallets, and the spring offering scarcely any resistance in the
neutral position (unlike a heavy pendulum) the force of the
escapement is suflBcient to move the balance through the
angle of escape ; and having once begun, it wiU of course
go on. Hence it is that with. most escapements a watch
cannot be stopped, if it is clean and in good order ; for as
the impulse is generally given at the neutral position of the
spring (as it ought to be, for the same reason as in clocks).

VERTICAL ESCAPEMENT. 1*5

the force requisite to give tKe impulse is generally sufEicient
to start the balance. The same thiug happens in a clock
when yon take the pendulum off, and the esci^ement has
only the slight weight of the crutch to move.

lis. The spiral aprings used for escapements are of two
kinds; the common one lying all in one plane, and the
other, used for chronometers, in which size is not sacrificed
to degance, is like a wire wrapped round a cylinder, as the
string of a dock ia wrapped round the barrel ; since this is
found to be the best form of the two, perhaps on account of
every ring (so to speak) of the spiral having the same radius,
and the sprii^ acting therefore more uniformly.

114. The kind of watch that 1 have been describing is
the old vertical watch, so called because the scape-wheel
stands vertically when the other wheels are horizontal, or
the watch is lad flat. This kind of escapement, as before
mentioned, lite the common recoil escapement in clocks
with anchor pallets, loses as the arc of vibration decreases.

REGULATION OF WATCHES.

115. The mode of regu-
lating this and all watches
is by altering the fixed point
of the spiral spring, so as
to make the acting part of
it shorter or longer, and
therefore faster or slower in
its vibrations. This is done
as follows. A B D is the

14|B WATCHES AND CHBONOMETEES.

springs or rather a portion of it^ as I have stopped it at D
to avoid confusion. The outer end of it is pinned into a
cock set on the firame at A. The pointer C B E turns on
an annular or hollow pivot at G, the hole being left in ltd
oentre for the arbor of the balance^ which is called the verge,
to go through. At B there are two small pios close to-
gether^ between which the spring is passed^ and which
therefore determine the point from which it begins to bend.
Therefore as the pointer or regulator G B £ is moved towards
the right in this drawings it makes the spring vibrate fester^
and to the left^ slower ; and this is done without affecting
the neutral position of the spring. If the watch still goes
too slow^ when the regulator is moved to the right as far as
it can go, the spring has to be taken out and shortened by
putting the outer end farther through A and drawing the
inner end farther out through the other cock by which it is
pinned to the balance ; for as a given angle corresponds to
a smaller length at the inner end of the spiral than at the
outer, the spring will on the whole be shortened by this
operation, while the neutral position of it with regard to the
balance remains the same. In order to alter the length of a
cylindrical spiral spring, either its curvature must be altered
a little or the point at which it is attached to the balance.
But, in fact, chronometers are not regulated in this way, but
by altering the in«rtia of the balance by screws with heavy
heads, called timing screws. The vertical escapement ii
only now used for the commonest watches, both on account
of the thickness it requires^ and its inferiority to other
escapements.

147

LEVEE ESCAPEMENT.

116. The escapement which is far the most frequent
in good English watches is the lever escapement, or, as it
used to be called, the detached lever, to distinguish it from
another form of it, now disused, called the rack lever. If
you put a rack, or a few teeth of a wheel, of which the
pallet arbor would be the centre, on the end of the crutch
of a clock dead escapement, and let this rack work a pinion
set on the verge of a balance, such as I have just now
described, the vibration of the balance would cause the
pallets to move -as they do under the influence of a peridti-
lum. And this was the rack-lever movement.

117. It was however liable to stop if the balance was
accidentally stopped at the neutral position, on account of
the friction between the rack and the pinion ; and moreover
the lever or crutch and pallets were carried farther the far-
ther the balance vibrated. This as we have seen cannot be
helped with a pendulum, on account of the small angle
which it moves through ; but it can with a balance, since
that moves through such a large angle that the arc des-
cribed by a pin set a little distance from the verge will cut
the arc described by the end the lever so as to include a
very sensible depth between them. Consequently if the
end of the lever merely has a nick in it, and the verge in-
stead of beiDg a complete pinion has one tooth or pin that
will fit into the nick, the lever and pin will act together as
a wheel and pinion for a short distance in the middle of the
vibration, but as soon as the pin has got out of the nick
the balance may turn as far as it pleases without moving or

H 2

HS WATCHES AND cnRONOMETEBS.

being even in contact with the lever; and when it returns the
pin wiU go into the nick again and first move the dead part
of ihe pallet off the tooth of the scape- wheel, and ^sa receive
the impulse and leave the opposite pallet with a tooth test-
ing upon its dead part. Therefore this waa called the de-
tacked lever, as the lever is detached from the balance except
during the middle of the vibration. The pin is usually
made of a jewelj and it works with so little friction that
Tou can hardly (if at all) stop the watch, vxj more than a
clock with a dead escapement when the pendulum is taken
i)H'. The pallets are also always made of jewels in good
watches. In
this drawing
the balance is
put beyond
its real dis^
tance from the
scape-wheelin
order to show
theother parts
more plainly:
it is exhibited
at the middle of the impulse. The practical advanti^s of
tills movement are that it is not only avery good one, being
like the dead escapement of a clock, uid without the dead
friction, which is very nearly removed by the detachment of
the balance from the pallets, but it is moreover easy to make
iind safe t« wear ; and if the watch gets such a Ml as to
break the ve^, which is always the first thing to break,
it can be mended for a few shillings, the verge in this

HOEIZONTAL ESCAPEUZNT. 14>9

escapemeat being Dotbing more tban a plain arbor^ wbich
camefl the pin set upon a small collar. Whereas in the
two nest escapeHwnts the vei^ itself is comparatiTely com-
plicated, and expensive to make and mend.

HORIZONTAL ESCAPEMENT.

118. It is curioos that this, which was invented by an
English clockmaker, Oraham, is the escapement pnt to nearly
every foreign watch, whereas the rack lever, which was the
foundatioii of the detached lever, the principal English es-
capement, appears to have been invented in France, though
the detached lever was invented by Mudge, a famons chro-
nometer maker here. There. is nothing in clocks correspond-
ing to this escapement, and it will be best understood at
once &om the drawing. The vei^ is spread out about ils
middle into a portion of
a hollow cyhnder, of
which the section is
sliown at Afi. The
scape-wheel teeth are of
the shape of a ' flat iron'
set upon a pin, as shown
in the second flgore, and
just long enough to be
contained with the cy-
linder. A tooth is here
represented as just es-
caping iiom the inside of tue cjlmdet and giving the iiu-

150 WATCHBS AND CHKONOMET£ES.

pulse ; for as the balance turns to the right"^ the sloped part
of the cylinder at A comes up to the point of the tooth,
and so the tooth in making its way out, gives an impulse to
the balance ; and then the next tooth strikes against the
outside circular part at B, and rests on it until the balance
turns the other way, and then that tooth makes its way into
the cylinder giving an impulse in so doing; This escapement
therefore is not detached, as a tooth is always pressing
either upon the inside or the outeide of tiie cylinder, and as
in the common dead escapement, a tooth is always acting on
the inside of one pallet or the outside of the other. This
is not unlike the pin wheel dead escapement in this respect^
that it is not very material that the teeth of the scape-wheel
should be exactly at the same distance from each other^
since they act successively. But is very unlike it in ano-
ther respect, that it is very expensive to mend if broken.

One curious fact in this escapement is worth mention-
ing : it is found that the sharp teeth of the scape-whed
cut the cylinder less if they are made of steel than of
brass. I have heard of no satisfactory way of accounting
for this ; and it seems that there is yet room for a good
deal of discovery in the theory of the wear of two metals
working together, in which several of the known facts are
different from what were anticipated, especially the necessity
for soft bearings, made only of block tin, which is nearly as
soft as lead, for railway axles orjoumah ; while on the other
hand I understand that brass, aind even gun-metal, is aban-

* Perhaps it may be as well tO'explain, that a wheel is said to
turn to the right, when, if you took hold of it with your right hand
in its natural position, you would turn your thumb to the right.

DUPLEX ISCAPEMBNT. 151

doned for tlie bearings of lathe sprndlea in fevoor of cast-
iron or steel. There is no doabt, however, that iron and
Bted working together reqtiire freah oil more frequently than
brass and steel; and brass scape-wheels are nearly always
used for the dead escapement in clocks, and the lever
escapement and all others except the horizontal in watches,
which is just the one in which we should have expected the
points of brass teeth to be worn out sooner than in any
othex, instead of wearing the hard cylind^.

DUPLEX ESCAPEMENT.
119. The daplex escapement is so called because the
scape-wheel has a doable set of teeth : viz., a set of long
teeth, which merely rest gainst
the verge of the balance except
when they are escaping, and a
8C(t of short teeth or pins to
give the impulse at the time of
escape. The long teeth are so
made that their forward edge is
a radius of the scape-wheel and
a tangent to the small circle

with a notch in it j consequently

that circle or cylinder, which is a portion of the vei^e, can
torn to the right, with no other effect upon the long teeth,
than that the friction against th^ is rather greater as the
opening of the notch passes, than when they are merely
pressing upon the cylinder ; but as the cylinder is very
■small, and the teeth long, and the notch narrow, this extra
friction is very little. When the balance returns, the point
of the tooth Ms into the notch, and goes along with it, and

152 WATCHES AND CHROKOMETERS.

SO escapes^ and at the same time one of the pins catches the
long tooth projecting from the verge^ and gives the impulse.
It will be seen that the principle of this escapement »»
not unlike that modification of the dead escapement for
clocks^ which I suggested (45)^ and which if it can be made
accuratdj enough with moderate care^ ought to answer
equally well ; for here the dead friction is that of long teeth
acting upon a cylinder of small radius^ while the impulse is
given by short teeth acting against a long radius. !For this
reason^ and also from the action being so direct that it
does not require oil^ the duplex escapement is a very good
one; but^ as may be inferred from this description of it^ it
requires unusual care in making and putting together, and
also in carrying about ; for if, by an accidental twist of the
watch^ the balance should h^^pen not to vibrate tax enough
to let the notch get past the long toothy the escape cannot
take place^ and the balance loses its impulse for that vibra-
tion ; and as it only receives an impulse at every alternate
vibration, unlike the three preceding escapements, it will
probably not recover itself and will stop. It is therefore
unfit for ordinary wearersof watches, and above all for those
who in winding up their watch turn it nearly as much as^
they do the key : a very mischievous practice with any good
watch, as it deranges the arc of vibration for the whole time of
winding up, and some time afterwards. It is not perhaps very
easy to avoid it altogether with an ordinary key; and there-
fore I should recommend persons who have really good
watches to get a key made with a straight wooden handle
like a thickish pencil. You can then wind up your"
watch, keeping it quite steady, by a few twirls of this
pencil between your finger and thumb, and in a quarter of

CHaONOMETBBS. -loS

tix time that a common key takes. Tb.e watchmakera them-
selvea always use these pencil keys.

CHRONOMETERS.
120. The perfection of all the watch eacapemeiito is
tliat which has from its use acquired the name of the
chronameter movement, but was originally called the de-
tached, the balance being entirely detached from everything
else except just at the time of action : in other words there
is no dead Miction; and moreover the impulse is given
direcUy, and nearly at right angles to the line of centres of
the balance and scape wheel, as in the duplex escape-
ment, instead of obliquely as in the vertical, lever, and
horizontid esca^meuts ; and therefore it is not subject to de-
rtmgemesit fay Uie variable stale of the oil, as it requires none.
The teeth of
the scape-
whed, in-
stead of rest-
ii^ against
a verg^ rest
against a
stop S set
upon a lever
a b. This
lever having
only to move

through a very snmll angle is set upon a small and stiihsli
spring at a instead of a pivotj which allows it to move just
as a pendulum spring doea a pendulum. The other end of

154 WATCHES AND CHROJfOMETEfiS,

the lever has a weaker spring h also screwed to its inr
side .(that is the side nearest the scape wheel) and pro-
jecting a little beyond its end. On the verge there is a
small tooth or cog c which can pass the spring in the
direction towards the scape wheel, by merely pushing it
aside as shown in the enlarged drawing of that part, as it
has room to bend in that direction; but in going the other
way the spring cannot bend, and therefore the tooth c
carries the lever with it, moving on its own spring a; and
in so doing the stop S is pushed out of the way of the tooth
of the scape wheel, which is therefore let go ; and at that
moment the long tooth or snail end attached to the verge
(which corresponds exactly to that in the duplex escape-
ment), comes into such a position that the tooth of the
scape wheel catches it and gives the impulse.

It is evident that this also is an eseapement that re-
quires considerable care in making and using. However
it is never applied to any but chronometers, or the very-
best watches, and those of considerable size, and persons
who possess them are aware that they are instruments of a
very different class from an ordinary watch. It is men-
tioned in the Encyclopsedia Britannica that a maker of
the name of Owen Eobinson made use of long teeth for the
stopping part, and short ones for the impulse, as in the
duplex escapement, but the contrivance has not been gene-
rally adopted. Probably the friction of unlocking the
common teeth is so small that the two sets of teeth were
not worth the additional trouble, and the long teeth in-
creased the inertia of the balance.

121. It may be observed that as the lever is not conn-

CHRONOMETEES, GIMBALS. 155

terpoised^ tbe work to be donje in unlocking is different^
according as the watch is placed vertically with the weight
of the lever pressing towards the scape wheel, and therefore
having to be lifted at unlocking, or the other way up, when
the weight of the lever helps to unlock it, or horizontally,
when the weight acts neither way. Consequently it is desira-
ble to keep a chronometer always in one position ; and that
position is the horizontal one for another reason, which
applies to several things besides chronometer balances.

If you take a small portable clock with a balance
heavier than any watch balance, and lay it on its back ot
side, and observe the vibrations of the balance, you will see
that they are much less than when the clock stands up, so
that the balance is horizontal. The reason is that a pivot
standing upright and with its point resting on a hard
surface, and merely kept in its place by the hole in which
it is placed both at the top and bottom, moves with much
less friction than the same pivot set horizontally in circular
pivot holes. Por, however thin the pivot may be made,
of course its point can always be made smaller, and in fact,
if the wheel is Ught, it may approach indefinitely near to a
point, in which case there would be no friction, at least none
which the weight of the pivot and its wheel would augment,
the lateral friction against the sides of the hole being inde-
pendent of the weight resting on the vertical pivot. Ship
chronometers are accordingly kept horizontal by being hung
in gmbala (see. next page), which are in fact an universal
joint, the chronometer having two pivots E, W, which move
in holes in a large ring having other pivots N, S, at right
aligles to E, W, which turn in holes in the sides of the box.

166 WATCHES AND CHRONOMETEffiS.

The fly of the stziting
part of very large clocks
is in like maimer some-
times placed with its axis
vertical, being connected
witli the train by bevelled
wheels, partly in order to
avoid the friction on the
pivots of such a heavy fly
movingwith great velocity,
and partly to save room.

122. Another remarkable application has latdy been
made of this principle of nsing vertical pivots ; viz. in the -
ship compass. Everybody knows the common way of doing
it, viz., fixing the card and needle upon a conical cap, or in-
verted cup, standing on the top of a sharp spike. Thia, <d
course, has very little friction, when merely revolving level;
but then it is liable at sea to great disturbances which some-
times render it useless ; and moreover these vertical oscilla-
tions soon wear the point blunt. Mr. Dent has therefore
lately applied the chronometer suspension to compasses;
that is, the axis goes right through the card like the axis or
ve^ of a watch balance, and rests at the bottom on a
jewel or hard piece of steel put under the pivot hole, and
at the top in an ordinary pivot hole set in a frame above
the card, the whole apparatus, as usual, being swung in
gimbals in the same way as the chronometer just now des-
cribed. There appear also to be several collateral advantages
in this kind of suspension besides its steadiness ; such as
the power of making the compass as tiuggUh as yon please

CHRONOMETER SUSPENSION FOR A COMPASS. 157

by means of an adjustable spring pressing against the side
of the upper pivot, and the power of inverting the compass
to ascertain the error of colUmatian. , However, it wonld be
out of place here to dwell at any length on the compass
suspension, which is only introduced as an illustration of the
principle of suspension of the marine chronometer.

I said just now that the lower pivot of this compass
rests on a hard piece of steel or a jewel. In the escapement
of all good watches, and in the best clocks, there are what
are called end-steps; that is, the pivots are not kept in
their place endways by their shoulders, but by stops, of
metal in clocks, and jewels in watches, against which
the pointed ^ids of the pivots rest, not of course tightly,
but suffi(»enfly dose to allow only the necessary shake
or freedom. The necessity of this freedom, both end-
ways, and sideways, of all the pivots in clock and
watch work, is one of the points in which it differs from
common engineering; for in other machines there is
generally force enough to spare, so that a slight degree of
tightness in a pivot does not signify, especially if plenty of
oil is used. But in the going part of a clock such an
occurrence would probably stop it. Besides the end-stops,
the pivot holes for the balance, and the scape-wheel, are
made in jewels in good watches ; and beyond these there
appears to be no use in jewelled holes ; and watches that
are called jewelled in eight or ten holes are often inferior to
those which are only jewelled in the four I have mentioned.

NEW STOP WATCH.
123. It requires some experience and quickness to note

158 WATCHES AND CHRONOMETEES.

the exact second at which any phenomenon takes place
which you have to employ your eyes upon. Astronomers
do it by looking at tl\eir clock at some given second^ and
then counting the beats from it by ear as they look through
the telescope ; and experienced persons can do this to a
t^ith of a second. But for the purpose of making this
more easy to ordinary people, watches have been lately
made with a large second-hand, carrying some colouring
fluid on its end; and there is a small pia which you
press with your finger at the. moment when you observe the
phenomenon, and this presses the point of the second-haad
upon the dial, and so makes a mark, which you can after-
wards examine at your leisure, and without the necessity of
employing your attention on counting the seconds. The
same thing used to be done by the pin stopping the watch
when it was pressed, which of course made it wrong after-
wards. In a stop watch, of either kind, you can only
denote the time to that fraction of a second, which the
scape-wheel happens to beat; and therefore a watch with a
lever escapement will be better for this purpose than, one
with a detached or duplex movement, since in them the
second-hand only moves at every alternate vibration of the
balance.

In other respects watches differ so Uttle from clocks in
the principles of their construction, that it is unnecessary to
say any farther on that subject. But there stiU remains to be
noticed a condition which is even more essential to the
accuracy of their performance than to that of clocks. I
mean the

159

COMPENSATION OF THE BALANCE.

124. The balance of a watch requires compensation
much more than a pendulum^ if it is to be exposed to
such changes of temperature as chronometers are^ though
watches carried in the pocket are not subject to much vari-
ation of that kind^ unless they are left exposed in cold
nights. The variation in the elasticity of the spring, which
affects in a small degree the vibration of a heavy pendulum
whose time is mainly determined by gravity (65), affects a
light balance whose time of vibration is mainly determined
by the force of the spring a great deal more. I extract
from a smaU pamphlet on compensation balances, published
by Mr. Dent, the following results obtained from a glass
disk as a balance, which was used for the experiment
on account of the moment of inertia of such a disk being
less affected by temperature than a metallic one.

Temp^atL. Yibrations in au hour.

32« 3605-7

66*^ 3598-2

100^^ . . . . - 3589-7
(The proper number being 3600). Supposing, therefore,
that the balance had been adjusted to go right at 32^,
it would have lost 7*54 and 8-5 seconds respectively for
the first and second increase of 34^, which is equal on the
average to more than 3 minutes in the day; whereas we saw
(57) that a common iron wire pendulum would only lose 10
seconds in a day, with about 1^ more for the spring, under
such an increase of heat of 34^. And if a metal balance
had been used instead of a glass one, the loss would have

160 WATCHES AND CHRONOMKTERS.

been still more^ on account of its expansion. I believe it is
not far from the truth to say that the effect of the expan-
sion of the metal in a balance is as much less than that of
the weakening of the springs as the effect of the weakening
of the spring is less than that of the expansion of the sted
rod in a 1 sec. pendulum. Any body may easily satisfy himself
that the variation in the elasticity of a watch-spring vastly
exceeds in effect that of the spring of even a short pendu-
lum^ by putting a common watch and a bracket*clock with a
pendulum together in a cold room in winter, and adjusting
them (if necessary) till they go pretty well together ; then
shut them up in a hot room for a day, and you will see that
the watch has been left; several minutes behind by the dock,
in consequence of the greater effect of the heat upon the
balance spring than upon the pendulum spring ; for as far
as the expansion of the metals is concerned, the balance and
the pendulum rod will expand about equally.

125. The difference in the amount of compensation
required by a balance and a pendulum is so great, that it
cannot be effected exactly in the same way, though all the
methods that have been invented depend upon the same
principle, of making small weights attached to the balance
approach nearer to the centre as the heat increases, so as to
diminish the moment of inertia, or the resistance to the
force of the spring.

It is true of a balance, as of a pendulum, that if
it were composed of rods or spokes without weight and
a rim consisting of a single heavy line, or even a line with
weight in only one point, the tiine of its revolution would
depend (the force being the same) solely on the square of

COHPENSATION BALANCE. iOl

the radios of the rim. Bat aa the mere expansion of the
wheel itaelf prodnces a small effect compared with the
decrease of force in the spring, it is evident that we most
have some more violent method than the ttraight fincaTd
expansion of one metal over that of another, which will do
in a pendulum, to produce the requisite effect in a balaoce.
And this effect is produced accordingly by the curvilinear
expansion of one metal upon another.

If you fasten together tightly, as by soldering, a bar
of iron and of brass, and heat them, the brass expanding
more than the iron will evidently bend the iron inwards.
The way, therefore iu which a compensation balance
is made is this. A ring of steel is made with a bar
across the middle; outside the ring is cast another
ring of brass in such a way as firmly to adhere to
tile steel, in fact to be brazed to it; this ring is then
filed up to the proper size, and then a broadisb cut is
made through both rings at each
of the comers A, B ; and finally a
few screws with heavy heads are
set in various places near the end
(rf each portion of the cut ring.
Consequently, as the heat dimi-
nishes the force of the spring, it
expands the outside brass curves
more &an the inside steel ones, and so their ends, with the
additional weight of the screws, bend inwards towards the
centre of the balance, and its moment of inertia is dimi-
nished. The proper adjustment of these screws is, as may
be supposed, a very delicate operation, and requires a great

162 WATCHES AND CHRONOMETBRS.

many trials at differeut temperatures^ and can therefore only
be done in winter^ or by means of freezing mixtures ; and
is consequently very expensive. And many watches with
compensation balances are sold^ which have never been ad-
justed at all, and nobody can tell by merely looking at
them whether they have or not. They may be somewhat
better than completely uncompensated balances, as the
screws have probably been put in according to the common
rules for a first approximation; but this is a matter in
which no security can be had except the reputation of
the vendor, unless he will allow the watch to be taken away
and tried in different temperatures: any person, of ordi-
nary observation, who has the means of resorting to a
good clock can easily try whether the compensation is
tolerably complete, or is over-done, as it sometimes ia.

A similar contrivance has been applied to compensate a
pendulum : two compound rods of this kind, with the brass
«ide downwards, being made to project from the bob, and
carry balls at their ends, which therefore rise as the bob falls
and the brass expands. They have, however, never come
into general use, aad all such projections from a pendulum
are objectionable on account of their tendency to twist if not
placed exactly in the plane of vibration; and it would be
unsafe to trust to a compensation of this sort without actual
trial, which would make it at least as expensive as a zinc
compensation; and on a large scale the compound bars
would probably split themselves asunder instead of bending.

SECONDAEY COMPENSATION.
126. Still however the compensation is not completely

SBCONDARr COMPENSATION. 163

e£Eected in this way. It has been fonnd that if it is ad-
justed for two extreme temperatures^ such as S%^ and 100°,
the watch will gain at mean temperatures, and if adjusted
for mean it wiU lose at extreme temperatures. The reason
is this. The force of the spring is ascertained to vary as the
temperature ; but the isochronism at different temperatures
depends upon the ratio of the force of the spring to the
inertia of the balance remaining the same, just as the time
of a pendulum depends upon the ratio of the force of
gravity to the radius of oscillation. Now by the ordinary
method of compensation the weights approach the centre at
a rate nearly proportionate to that of the increase of tem-
perature, in fact rather more rapidly at low temperatures
than high ones, which is just the reverse of what is wanted.
Por the inertia of the balance depends on the s^are of the
distance of the weights from the centre; and therefore in
^er that it may always bear the same proportion to the
force of the spring, the distance of the weights ought to
vary more rapidly when they are near the centre than when
they are far from it, that is more rapidly at high tempera-
tures than at low ones.

-To persons accustomed to mathematical formulae the
nature of this result will be clearly exhibited by observing
that if r be the distance of the weights M (which for con-
venience we may suppose to be the whole mass of the
balance) from the centre, the new moment of inertia, for
an increase of temperature which causes an increase of r
which we may call dr, will be Mf r'^- 2 ro[r+ d/j ; or the

ratio of the new inertia to the old will be 1 + —^ — f- ( T/ •

164

WATCHES AND CHRONOMSTERS.

The reader may remember tliat in the case of com-
pensated pendulums we neglected the quantity corres^

jtonding to (— ) because of its smallness ; but the com-

Iiensation required for a balance spring is so much greater
than that required for the expansion of a pendulum rod^

that the effect of the term ( ^ j now becomes sensible ;

for^ as was stated before^ the object of these compound bars
of balances is to make r vary much more rapidly than it
could do if the metals acted only by their direct expan-
sion. And it is this term yy) which renders necessary what

is called the secondary compensation, which is of course a
great deal smaller than the primary one which is represented

by ^-ZL , but stiU is large enough to require a special contri-
vance in very accurate dironometers.

127. Or to adopt the illustration given in the pamph-
let I have referred to, the variation in the force of the
spring may be represented by a straight line ABC in-
clined to the straight line of temperature at an angle re-
presenting the ratio at which the primary compensation

must advance; where-
as the variation in the
inertia can only be
represented by a curve
such as A £ C, which
can be made to coin-
cide with the straight
Une at any two points

SECONDARY COMPSNSATIOK. 163

ve please, but at no others. This figure will show that if
we make them coincide at extreme temperatures the curve
fells below the straight line at the intennediate t«mperstures,
or the inertia is too little for the force, and the watch will
gain ; whereas if we adjust it for any two adjacent tem-
peratures it will lose for all above or below them.

128. Several contrivances have been adopted to effect
this object of making the weights move faster when they
are nearer the centre. It will be sufficient to describe one
of them in snch a way as to show the principle of their
construction, which is, if compound bars are used, to give
them such a curvature as will oarrj the weights at the ends
in a direction more nearly coinciding with a radius of the
wheel when they are nearer the centre than when farther
from it. It will be easily seen from tliis drawing that if
the curved pieces are made of

brass and steel, with the brass
inside the curves, they will
carry the weights inward as
the temperature increases, and
that the motion will be more
in a radial direction when they
are comparatively near the
centre than when far from it.

129. The method just now described is Mr. Dent's-
It appears from a report of the astronomer royal to the
Admiralty, in a parliamentary paper lately published, that
the same thing was done to a certain extent and the
principle of it suggested by a Mr. Eiffe ; and that it has
lately been done with great success by Mr. Loseby (several

166 WATCHES AND CHBONOlilTEBS.

of whose chronometers have been accordingly purchased
for the Admiralty) by means of mercurial tubes^ curved so
that the expansion carries the mercury outwards, when its
extremity is near the centre, more rapidly than it does when
the mercury has reached a part of the tube more distant
and more curved towards the centre. I have no means of
giving a correct drawing of Mr. Loseb/s compensation
tubes, but the principle of their operation is sufficiently
evident.

END OF CHAPTER II.

167

Chaptbe in.

ON CHUECH OR TUERET CLOCKS.

The principal diflFerence between church or turret clocks
and house clocks is in their size. But this difference makes
it necessary to attend to some things in their construction
which hardly require consideration in small clocks. More-
over they cannot always be made in the same way, because
they have to adapt themselves to various situations, and
have very different amounts of work to perform, and are
required to satisfy very different conditions as to accuracy
and price.

PENDULUM.

130, In all cases, however, the first thing to attend to
is the steadiness of the suspension of the pendulum ; which
may vary in weight from 1 to 3 or 4 cwt., according to the
size and number of dials that the clock has to work. No
rule can be laid down upon that point ; but for the reasons
stated in § 39 the pendulum ought always to be as
long and heavy as it convenientiy can be, and the greater
the amount of friction, and therefore variation in force, the
train is Uable to, from large dials, the greater necessity there
is for a powerful pendulum. And the heavier and longer

1G8

CHURCH OR TURRET CLOCKS.

the pendulum i&, the more it will require a firm support ; and
this is generally best obtained by fixing the cock which
carries it to the wall behind the clock. The cock should
be cast on a large iron plate^ which is fixed by bolts leaded
into the wall. The bolts should have shoulcfers to receive
the plate^ or else screwing the nuts on will tend to draw
them out of the wall, And the bolt holes in the plate
should be large enough to allow some motion for adjust-
ment. For cheap clocks the cock may be merely a strong
piece of cast iron^ leaded into the wall^ with a proper
opening in it wide enough to carry the spring and cAope
in the manner described for astronomical clocks (26)^ which
is the only way of fixing the top of the spring firmly.
But care should be taken to put the cock in so that the
pin through the chops will lie quite level and also parallel
to the wall, or at right angles to the pallet arbor, and only
so much above it that the bend of the spring will come just
opposite the end of the arbor.

131. The spring should be broad and thin, not
narrow and stiff, and not more than 4 or 5 inches long,
from the chops to the pendulum top.* Sometimes, to
prevent the pendulum from twisting, two narrow springs
are used, separated by about an inch. But a single one,
broader than the two together is better, not only because
it ^tU affect the vibrations less by its own elasticity, but
because, if the two springs are not exactly of the same length

* Mr. Dent has found he can get from the saw-makers better
pieces of steel for turret-clock springs than from professed spring-
makers, and at half the cost. I have seen some specimens of each,
and there is no question which is the best.

PENDULUM SDSPHNSION. 169

and atrengthj they will tend to twiat the pendulum at every
vibration. The chops may be as well of cast irou as of
brass, and they should be screwed together through the
spring as near the bottom as can be. In this drawing I

have shown the chops and spring and a side view ol the
cock and the plate belonging to itj and the lewises of the
bolts. I have also given a front view of the fonn of plato
which appears to me the best for obtaining steadiness with
four bolts.

132. Of coQise a compensated pendulum is better than
an uncompensated one; but the expense of compensating
a 14 -feet pendulum is an obstacle to their use. The Ex-
change clock is the only one in England, if not in the
world, with a compensated pendulum of that length. Mr.
Dent, however, has lately begun to use 8 feet pendulums
compensated, with bobs of nearly % cwt; and it appears
that such pendultmis do not cost above £7 or £8 more thau

170 TTRRET CLOCKS.

a wooden one equally well made. It may be as well to
remark that cast tubes of zinc are not found sufficiently
solid to expand and contract as they ought to do; and
consequently it is necessary to make the compensation
tubes of se\F^al tabes oi the common sheet zinc soldered
together, in order to obtain sufficient strength to carry a
heavy bob without bending.

133. If the pendulum is made of wood, whether deal or
mahogany, it should be as straight in the grain as possible^
and free from knots, and not above half an inch thick and
two inches wide (which is strong enough to bear several
tons); for the thinner it is, the less the weight of the rod,
and therefore the radius of oscillation of the pendulum, can
be effected by its absorbing moisture, and the straighter the
bob will keep it if it has any tendency to bend. It should
be dry and well varnished several times over, and the ends
ought to be well saturated and aH the screw holes, to keep
out the damp. The wood should reach as near both to the
top and the bottom of the pendulum as the necessary metal
terminations will allow ; and with that view, perhaps, it
is better to make the crutch with a pin to go into the pen-
dulum rod than with a fork : the pin should be adjustable
for beat in the end of the crutch. The pendulum should
end in a point, and should have a degree plate under it
marked to about 10'. It may be convenient to state that the
length for a degree on the plate is very nearly -^th of the
whole length of the pendulum, and no very great accuracy
is necessary, as you only want to see how much the arc
varies.

When an eight feet pendulum is used, it is generally

PENDULUMS. 171

better to elevate the clock, so that the pendulum is wholly
within the chamber, than to let it hang down in a box
below ; for otherwise the bob cannot in most cases be easily
got at to regulate the pendulum, or to observe the arc it is
swiliging, which affords an indication whether the clock
wants cleaning or not. There can be a moveable pair of
eteps or platform to wind up by, which when not used will
go under the clock, and so take up no room, as a fixed plat-
form would. I may add, that the screw for raising the bob
ought always to be at the bottom of the rod, and not at the
top, or, still worse, at the side of the bob. In a compen-
sated pendulum it would, as a matter of course, be put
at the bottom ; and in a wooden one it caonot be put at the
top without making part of the rod of metal ; and if it is
put, as it sometimes is, at the side of the rod, a little way
above the bob, altering the screw has a tendency to bend
the rod, so that the bob does not hang vertically upon it.
Care must be taken in making compensated pendulums,
both that the bob and compensation tubes do not turn with
the nut, and also that when you hold the bob steady, turn-
ing the screw does not turn the rod, and so twist the spring;
and therefore the zinc tube must not rest on the nut, but on
a collar, which slides on a square or some other uncircular
portion of the rod, and the collar and the nut should present
convex surfaces to each other, to allow the nut to turn more
easily. Bespecting the shape of the bob, and the method of
adjusting, I have already spoken in § 70, 71.

134. There is a practice, not uncommon with country
clockmakers, of hanging the pendulum to the wall at the

side of the clock instead of behind it, and connecting it

I 8

172 TUREET CLOCKS.

with the crutch (which sometimes goes np instead of down)
by a horizontal rod two or three feet long. This^ though a
convenient arrangement in appearance, is a very bad one
for the performance of the clock ; for it is evident that the
friction, and the shake, of the two additional pivots must
tend to diminish the vibrations of the pendulum, or in other
words must require a greater force on the pallets to maLn-
tain the proper vibration; and therefore, by virtue of what
is stated in § 36, must make the dock go worse than if the
pendulum were suspended in the common way, just oppo-
site the pallet arbor. No doubt there may be cases in
,M.Ut ^ h^, po^bl. ..^.^.lo»g'pe.M^i.
any other way; and when it is necessary so to suspend it,
the horizontal connecting rod should be as light as possible,
and its pivots small and accurately fitted to the crutch and
the pendulum, so as to diminish the friction and the shake
in the pivots as much as possible. Moreover, care must be
taken that the crutch and the pendulum move exactly in
the same plane, or the impulse of the pallets will tend to
make the pendulum revolve in a sort of elliptical cone, in-
stead of vibrating in a pkne.

135. If the pendulum cannot be fixed to the wall, or if
the clock frame itself is very strong and firmly fixed, it may
be hung from a flat iron bar going over the top of the
frame, and having a nick in the end broad enough to admt
the chops. This bar will have to be screwed into both the
back and front of the frame, and before the screw holes are
made, it should be carefoUy adjusted, so that the pendulum
will swing exactly in a plane at right angles to the pallet-
arbor, and having the edge of the spring exactly opposite

FRAME. ITS

to the end of the pallet-arbor; which may be effected by
taking out the arbor^ and looking through the two holes in
the frame at the springs and seeing that it is in the middle
and appears merely as a line.

FBAME.

136. It is of nearly equal importance that the frame
which carries the wheels should be strong and steady. The
frame of astronomical and house clocks consists merely of
two plates of brass joined together by pillars at the comers.
The frames of turret clocks are made of iron bars so placed
as to carry the arbors of the wheels. The old fashioned
way is to make the frame consist of a front and a back set
of bars joined by pillars like a house dock^ and requiring
to be taken to pieces to get the wheels out when they
want cleaning. This is still done in second-rate clocks^
though it may very easily be avoided. The frame ought to
be so made that when once put together and screwed down
to its standi the substantial parts of it should never be
taken to pieces again ; and this is either done by making the
bars which carry the wheels separate pieces^ screwed on
to the more solid parts of the frame, or, what is better, as
regards the smaller wheels, by making the brass bushes
which contain the pivot holes to take out, and then the
wheels can be removed separately, at any rate sufficiently
to dean them. These loose bushes should have. their three
screws set so as to form an isosceles, not an equilateral tri-
angle ; for if they are at equal distances the bushes get put in
in different positions, and as the pivot hole is not likely to be
be exactly in the middle of all the screw holes, it gets dis-

174 TDRKET CLOCKS.

torted from its true place. If there are only two screurs
there should also be one steady pin^ for the same pxirpose*
The whole of the frame^ or of each side of it^ should be ca^
in one piece^ and the pillars should have broad shoulders and
strong threads and nuts to unite the two sides together, and
the frame should be from ^ to |th inch thick according to the
size of the clock. Then the two barrels may be set in sepa-
rate bars bolted to each side of the frame. All the rest of
the wheels may be inserted by means of moveable bushes
and without any extra bars to the frame. In this way the
frame is strongs, as well as cheaper to make^ than if it is
made in many pieces which have to be fitted to each other.
But there are several varieties of clock frames which it may
be as well to describe separately.

187. First suppose there are to be four wheels in the
train, as in a house dock, and all the arbors of the same
length as the barrel, this being the most ordinary kind of
construction. Then a frame such as this will be perhaps
the best said most compact form. I have inserted the end
of the bar which carries the pendulum, in order to show
how it is to be placed if the pendulum is not fixed to the
wall. I have not indeed seen a frame of this form> and
possibly the arrangement n^y be found on trial to require
some little modification; but a dockmaker to whom I sug*
gested it said he should use it; and when it is necessary
to resort to a four-wheded train, this kind of frame wiU
carry the wheels with a less amount of iron work than usuaL
F P P P are the four pillars, and a fifth might he inserted
in a large clock in the cross bar which carries the scape-
whed and the hammer lever, and which has the lo<ddng

TOUE-WHKBLED TRAIN.

plate set upon a atud outside. The aumbera of the teeth
which I have inserted aie of course arbitraiy, and may be
altered in the proper proportions.

I have put down the great wheel of the going part as
turning twice more in the week thui the striking great
wheel, because the striking part abnost always requires a
heavier weight, and therefore a thicker rope than the going

176 FOUR-WHEET.ED TRAIN :

part. The requisite thickness of rope can be altered by
altering the diameter of the barrel or the fall of the weight ;
or if the fall is limited by the situation the weight can be
increased and an additional pulley added. It is, however,
to be remembered that every extra pulley adds very con-
siderably to the friction and requires a still further addition
to the weight to overcome that friction. I was lately able
to take 401bs. off a striking weight by merely removing a
guiding pulley which had been needlessly introdu^d. It
is a matter of experiment what thickness of rope § given .
weight hanging by a single moveable pulley requires : a
good rope half an inch thick appears to be strong enough
for any weight that is ever put to such a clock j and con-
sequently the barrels need never be more than a foot long
in a clock of this sort, as it is not supposed to be one of
very large size.

138. If the striking wheel has eight pins, it must have
eight times as many teeth as there are leg^ves in the pinion
of the wheel above it, in order that that wheel (which I
called before the second wheel) may turn once for every
blow that is struck (see § 93) ; and the second wheel must
also drive the fly some exact number of times in each
revolution of its own, since in turret clocks the fly arbor is
made to carry the pin which is stopped by the detent D
when they have done striking, as before described, the fly
itself being set outside the frame and having arms a foot
and a half long or more to carry the fans, and therefore
moving much more slowly than in house clocks, where it is
within the frame. These arms are not rigidly fixed to the
arbor but to a socket which turns upon the arbor, and .has

STRIKING PART. 177

a ratchett and dick so placed that when the arbor is driven
by the clock it carries the tLj with it^ but when the dock
is stopped at the end of the striking the fly can go on
by its own momentum^ as it conld not be stopped sud-
denly without the risk of breaking something. It is this
motion of the fly over the ratchett-teeth which makes the
noise like winding up that may be heard in the tower after
a church clock has done striking.

In the above drawing the locking-plate or count-whed
B L is outside the frame^ and is driven by a small pinion
of 8 set on to the projecting arbor of the striking-whed.
The lifting piece A G D is set on an arbor which is within the
frame but projects through it and has the arm G B set on
to it outside^ which works into the locking plate. At F
there is a roller which rolls upon the circular plate with a
piece cut out of it fixed to the second wheel. The snail at
A on the centre whed raises that end of the lever, and
therefore depresses the other end, so that the pin in the
fly-stop slips past D and rests against E when the clock
'gives warning.' When the snail lets the end A of the
lever drop, the fly is set at liberty; and as the second
whed begins to move, the circular plate and roller depress
the lever so far as to let the fly-pin clear both the stops D
and £, and then the locking plate by means of the arm
B not only keeps the lever there but moves it a little
fiEurther in the same direction, merdy for the purpose of
taking the friction oS the second wheel which moves
quickly, and transfering it to the locking-plate which moves
very slowly. In fact the roller F is not strictly necessary,
for the locking plate alone might be employed to raise the

I 8

178 TURRET CLOCKS.

lever^ as described in § 93 ; but it is safer to have it raised
at first by a wheel that moves so quickly that the lifting-
piece is sure to be out of the way before the fly has made
one revolution. Of course the end A of the lever must be
made a little heavier than the otiier end.

THKEE-WHEELED TBAINS.

139. I have supposed each train to have four wheels.
But it is evidait that it will move with less friction if the
teeth can be so proportioned that there may be only three
wheels. Now if we assume that the centre wheel shall
tarn once in the hour, we can hardly make the scape wheel,
which is now to be the next to the centre wheel, turn in
less than four minutes, which however can be done where
there is a two seconds pendulum with a scape wheel
having sixty pins instead of teeth in it; but it requires a
large number of teeth in the centre wheel. In this case
the great wheel may remain the same as before. In the
striking train the second wheel is dispensed with, but a
longer fly is required; and if the number of pins in the
striking wheel remains the same the great wheel will also
remain unaltered. The locking-lever however will have to
be altogether worked by the locking-plate, which requires
very accurate adjustment of the nicks to make the lever
rise and fall exactly at the right time, and the locking-plate
must be large in proportion to the length of the arm C B
in order to raise it quickly enough. Altogether this is
rather a critical movement, though I have seen it answer
very well in well made clocks, such as Mr. YuUiam/s, who
geueraUy uaea it, as wdl aa the correspondkg going train.

TItRBE-WHEELED TKAINS. 1?9

140. But there is another way of making three-wheeled
trains^ which is better oh several accounts. First of the
going train : it is not at all necessary that the centre wheel
should go round in an hour; for there may be a subsidiary
wheel (i. e. a side wheel not forming part of the train)^ which
turns in the hour^ and drives the dial-work ; such a wheel
is in fact used in the three-wheeled train I have just now
described^ to reverse the motion; and an extra wheel of this
soit does not cause nearly so much friction as the introduc-
tion of another wheel and pinion into the train. Suppose
we make the great wheel to turn in three hours instead of
six or eighty as in the four-wheeled train; then^ if it has
120 teeth^ and the next pinion 12 pins or leaves^ the
second wheel will turn in 18 minutes, and if that has
108 teeth, and the scape-wheel pinion 12 as before, the
same pendulum and a scape-wheel with 30 pins only, or
an eight feet pendulum with 40, will do. This is the train
in Mr. Dent's large turret clocks, with occasional variations
of the numbers for particular purposes.

The subsidiary wheel, to be worked by the great wheel,
must be one-third of its size, so as to turn in the hour : the
manner of fixing titis wheel I shall treat of under 'adjust-
ing work.^ But if the barrel turns in three hours instead of
eight, it will have to make 64 turns in the eight days
instead of 24, and so will require a much greater length,
and if all the arbors are made of the same length as this long
barrel, it will make the whole machinery very heavy. In
order to get rid of this objection, what is called a^ double
frame is generally resorted to ; that is, the barrels and their
great wheels have their back arbors in the same frame

180 TBBRET CLOCKS.

as the rest of the wheels, bat the front or winding ap
arbors in a eepatate frame standing Home disttmce in front
of the &ame that carries the other wheels. Bj this anange-
ment the arbors of the other wheeb can be made lighter
even than in a clock with a short barrel.

There is another advantage in this aa regards the striking
part, viz., that when the great wheel turns so often as once
in three or even four hoots, the striking pins can be put on
the great wheel itself, as it is large enough to carry the 26
pins required for one-third of the twelve hours. The exact
number is indeed immaterial, except that the mote pins it
has the fewer coils of rope it will have to carry for the
eight days. Now it is evident that the striking will be
done with less waste of power when the power has not
to be transmitted through the pinion of a second wheel,
in which it loses considerably by friction ; I shall have to

THUKE-WHEELED TRAINS. 181

state afterwai'ds the surprising extent to which this loss of
power takes place. The wheel next to the great wheel can
then be made to raise the locking lever in the same way
as the second wheel does in the four-wheeled train. The
more turns the rope takes over the barrel the easier also it
is to wind up^ and the difference in moderate sized clocks
may be such as to save the necessity of having what is
called a jack to wind up with, which is generally required
for the striking part of clocks with short barrels, except
with small bells.

141. This apparatus may be either fixed or moveable.
If it is fixed, as it ought to be when required at all, the end
of the barrel opposite to the great wheel is made into a
toothed wheel K (in the drawing of the four wheeled train),
And by the side of it is put a smaller wheel or pinion J
which works into it; and instead of the winding square
being made on the arbor of the barrel, it is made on the
arbor of this pinion, which of course gives greater power
in winding the clock up, by requiring more turns of the
key or winch to do it. The pinion is sometimes made to
push backward and out of gear with the wheel when the
clock is not being wound up. The loose jack consists of
a frame contaming a wheel and pinion with the arbor of
the pinion squared to form the winding square : the arbor
of the wheel is a socket with a square hole in it which fits
on to the barrel arbor ; so that when the jack is applied
and made to rest on some part of the clock frame, it be-
comes (except that it requires a thicker arbor as will be
explained presently) just the same as if the wheel had been
set on the barrel itself, and the pinion in the clock-frame.

182 TUERBT CLOCKS,

The going part never requires a jack wheel to wind it
up except in veiy large clocks : but I am not sure that it
would not be better to apply such a wheel (I mean of
course a fixed one) more frequently, even where the weight
is not too great for a man to wind up without it ; because
the effect of having to wind up on the barrel arbor is that
it must be thick enough to carry a winding square strong
enough not to twist, and therefore that pivot requires to be
a good deal larger, and therefore has more friction, than
would be necessary if it had merely to carry the weight.
The two cast iron wheels that require to be added for
winding by a jack wheel cost very little, and the plan also
saves something, in the construction of the barrel arbor
and great wheel. By a little contrivance one winding
pinion might be made to apply to all the three barrel
wheels : indeed there is no reason why the winder itself
should not have that pinion, instead of a pipe, set on an
arbor, fitting into proper holes to wind up all the barrels by.

142. Loi% barrels however cannot always be properly
used; because if the rope does not hang down, but is
carried over a fixed pulley above or at the side of the dock,
and there is not a considerable distance from the barrel
to the fixed pulley, the rope wiU not run straight enough
off the barrel towards the end, but obliquely as shown in
the last drawing, and consequently, instead of travelling
along the barrel as the clock is wound up, it will turn back
again and overlap itself; and even if it does wind up without
overlapping, there wiU be so much rubbing between the
successive coils of the rope as will soon wear it out, and
will moreover render a heavier weight necessary. In all

LONG BARRELS. 188

cases where a fixed pulley is required^ it ought to be as far
as it can be placed from the clocks in order to diminish the
obliquity of the rope as much as possible ; I should say
tljat the distance ought not to be less than eight times the
length of the barrel

Sometimes in order to avoid long barrels the rope is
made to go twice over them; but this is a most abominable
practice; for the weight has of course more power when
the rope is coiled the second time over the barrel^ as that is
the same thing as making the radius of the barrel larger
by the thickness of the rope, and so the force upon the
dock is not uniform; and secondly, it wears out the rope
more than anything else that can be done to it. When
the position of the clock is such that the fixed pulleys
cannot be as far off as about eight times the length of the
barrels, the clockmaker should not be allowed to use long
barrels.

143. There are however two ways by which the advantages
of the long barrels may be obtained without their disadvan-
tages. The first is by using wire ropes instead of hemp j*
but great care must be taken that they are good, as there
are some very bad ones made ; and they should be tried for
some time beforehand with a heavier- weight than they will
have to bear, and above all by winding them up frequently,
or they will cause constant trouble smd expense after the
dock is put up. In this way very elegant clocks can be

* In the Windsor Castle clock Mr. Vulliamy used catgut ropes
(vire ropes were not then invented) ; but they are enormously ex-
pensive : he was told that 17,000 theep contributed their entrails to
compose these catgut lines.

184 TURKBT CLOCKS.

made^ ¥dth great strength in a small compass^ and with
only three wheels in each train^ and striking from the great
wheel. A picture of one is given in the frontispiece.

144. The second method is to put about twenty striking
pins on one side of the great wheel and another set half
way between them on the other side^ and make them raise
two hammers alternately: forty^ or even thirty^ are too
many for one side of any but a very large wheel made in a
particular way^ which will be described presently. Mr.
Dent, until he lately at my suggestion adopted this other
method, constantly used the two hammer plan, and it
answers very well ; and such clocks strike with much less
waste of power, even when made in cast iron, than the most
highly finished clocks with polished steel pins set on the
second wheel. A wheel of this sort with forty pins will
turn very nearly twice m the twelve hours, or thirfcy-one
times in the eight days, for which a barrel of moderate
length will be sufiB.cient, especially as a smaller weight and
therefore a thinner rope will do the work than in a train
striking from the second wheel.

145. Or again, cheap clocks with short barrels might
be made with about twenty pins on the great wheel and one
hammer, to wind up twice a-week : a condition to which a
good many clocks are practically reduced which pretend to
be eight-day clocks, from being so placed that they will not
go fuU seven days. And those who can only afford to
spend a small sum upon a church clock had much better
have a good one made in this way than a bad one to go
eight days.

In every clock the going part ought to go half a day

THREK-WHEELED TRAIN. 185

longer than the striking part, in order that, if it is for-
gotten, the clock may proclaim by its silence that it wants
winding up before any harm is done.

Lastly, the reader may be reminded that in calculating
the teeth and pinions required for driving the hour wheel
by the great wheel separately from the train, the number of
the teeth of the great wheel is immaterial ; for in that case
the hour wheel will evidently turn in the same time as if it
were put in the place of the great wheel. Suppose the
scape wheel turns in m minutes and its pinion has j9, leaves,
and let ti be the number of teeth of the wheel that drives
it, whose pinion has /?, leaves, and let ^ be the number of

teeth of the hour wheel : then :~^ must = 22 .

Suppose j?i = 8 and jOa=10 (which will be enough if
they are lantern pinions, though not otherwise) and m=2 ;
then if ^s=24, ^, must =100, and the second wheel will
turn in 25 minutes ; and if t^, the number of teeth of the
great wheel,=l44, it will turn in six hours, or will require
only thirty-two coils of rope for eight days. In this case
the hour wheel had better be made as a large lantern
pinion. And if the great striking wheel has twenty pins
or cams on each side raising two hammers alternately, as
above mentioned, an eight-day clock may thus be made
with only three wheels in each train, with moderate num-
bers for the teeth, and without requiring the scape wheel
to turn so slowly as in four minutes, and without resorting
either to long barrels or wire ropes.

146. When the great wheel is the striking wheel, the
second wheel must turn exactly one-half or one-third round
for every stroke, and the circular plate before described in

IM THREE-WHEELED TBAIK :

the four wheeled train must have two or three pieces in-
stead of one cut out accordingly, to let the roller on the
locking lever fall at the proper time. Moreover this wheel
will turn too quickly for it to work the locking-plate by a
wheel and pinion, as it would require at least 234 teeth on
the locking-plate wheel. If the clock is wound up by
a jack wheel as before described, the barrel will ride upon
the arbor of the great wheel, and that arbor may carry a
pinion or small wheel to drive the locking-plate, just as
the striking wheel of the four wheeled train did. Sut
when the weight is small enough to be wound up without
a jack, the arbor must belong to the barrel and not to the
wheel, and therefore cannot drive the locking-plate. Jh
that case it must be done in one of the following ways.

The most simple method is to set the pinion on the
great wheel itself : and in every case the wjieel or pinioii
that drives the locking-plate, if it is set on the striking
wheel, must have as many teeth as there are striking pins,
assumiag the locking-plate to have 78, or in the same
proportion. 2. Although the second wheel turns too
quickly to drive the locking-plate by a toothed wheel and
pinion, yet it may do so by means of a ratchett-whed on
the locking-plate and two gathering pallets, (like the com-
mon repeating movement, § 90) set on the arbor of the
second wheel: the locking-plate must also have a click set
over the ratchett to keep it in. its place when the pallets
are not acting. A third way is to make the barrel arbor
hoUow nearly up to the end which forms the winding
square, and make the arbor of the great wheel go into it;
so that the barrel arbor comes through the front frame.

STRIKING l^ART. 187

but the wheel arbor goes the back frame and carries the
pinion that drives the locking-jdate. This^ when it is well
done^ is a remarkably neat arrangement^ but it requires very
good machinery to bore the hole truly all down the barrel
arbor, and if it is not done truly it had better not be done
at all, as it is sure to stick fast. These short trained clocks
may of course be put in a frame of the same kind as the
four wheeled one of which I gave a drawing. But they
afford facilities for a more convenient arrangement, by
setting the going and striking parts, or at least the upper
wheels of them, in separate small frames, which screw on
to a large and strong horizontal frame cast all in one piece,
which may carry the great wheel of the striking part, and
indeed of the going part also.

The clock in the frontispiece is an example of this kind
of frame. The great striking wheel is carried by a large
cast iron cock on each side, bolted to the main horizontal
frame, the surfaces in contact being planed so as to fit
accurately. The second wheel and the fly arbor are carried
by a small triangular frame at each end, which screws on
to the main frame. The locking-plate turns on a pin or
stud set on the frame, and as there is a jack wheel to
wind up by, the great wheel arbor comes through the front
cock and drives the locking-plate. The great wheel of the
going part being lighter and smaller than the striking
wheel is carried in the same triangukr frame as the rest of
the going wheels ; but tiie scape- wheel and the bushes of
the second wheel are made to take out without removing
the great wheel or taking the frame to pieces. It is not of
much consequence whether the second wheel can be got

188 TUaEET CIX>CKS.

completdj out, or not^ for if the bushes are removed it
can be cleaned within the frame as well as if it was taken
out. The scape- wheel however^ and the pallet arbor, should
be made to take out completely, without undoing the frame ;
and for this purpose nothing is required but the bushes to
be fixed with screws instead of rivetted in, as there is always
room enough for the scape wheel to pass the second wheel.
147. I proceed to point out some other things which
require to be attended to in turret clocks, in addition to
those rehkting to clocks in general, mentioned in the first
chapter.

ESCAPEMENT.

The scape-wheel and its arbor, as before observed^
should be as light as it can be made of proper strength j
remembering also that the fewer pins or teeth it has tho
lighter it should be made, as it has to move farther at each
beat. The pivot of the pallet arbor ought to come close
up to the pendulum spring ; for if it does not, the force is
communicated to the pendulum with a tendency to twist
the crutch : no such effect will of course be visible, but the
tendency to it produces an unnecessary friction on the
pivot, and requires greater thickness and therefore weight
in the crutch to resist it. In the Meanwood clock the
crutch is entirely outside the frame, straight, thin, and
broad, and therefore as light as possible, the pivot being
set in a cock like that of a common house clock. Some-
times however the frame is so made that the pallets and
crutch could not be taken out if they were set in this way;.

CKUTCH — SPRING PORK. 189

and in that case the pivot should be set in a bnsh projecting
as far as the pendulum springs the crutch having a bend^
and springiQg from within the frame in the usual way. It
is to be remembered that the drutch is itself a pendulum
of which aU the weight is carried by the pivot holes, and a
heavy crutch and arbor produces considerable friction,
which, like all other friction, is variable, and moreover con-
sumes force, diminishing the arc of the pendulum like the
dead friction on the pallets, of which the effect has been
ahready explained.

Eor the same reason the pivots ought to be as small as
they can safely be made, and also with as little shake as
will let them move freely; and the crutch should be long
that little may be lost by the necessary shake of the
pendulum in the fork. Whether the crutch ends in a
fork embracing the pendulum rod or a pin going into a
hole in it, it should be made with some screw adjustment
to put the clock in beat. And in trying whether a clock is
in beat the pendulum should be allowed to move only just
far enough to let it escape, and then the smallest deviation
will be easily observed. It may be a convenient rule for
unprofessional clockmakers to remember, that in all cases
if the right hand beat {i.e. the beat heard when the pen-
dulum is at the right) comes too soon after the left hand
one, the fork wants moving to the right with reference to
the crutch, and vice versd.

148. A very neat contrivance has lately been introduced
by Mr. Dent into his turret clocks. It occasibnally happens
that if the pendulum is moved while the scape- wheel is
standing still without any force upon it, the end of one of

190 TUBRBT CLOCKS.

the pallets just catches the point of atooth so that it cannot
slide up the pallet, and the momentum of a heavy pen-
dulum is then certain to break the tooth. In order to
prevent this the two sides or prongs of the fork are set
upon springs, which tend to bring them together and ke^
them close to the pendulum rod, with a stop of the proper
thickness between them. The springs are strong enough to
give the impulse to the pendulum, but if one of the pallets
should be stopped, the spring on the opposite side of the fork
gives way and lets the pendulum go on. The reader may
fancy that a single spring in the crutch would do as well;
but it would not; for a single spring would not have suffi.
dent resistance boti wayB to communicate the impulse to the
pendulum without bending; therefore there must be two
springs, both in a state of tension in opposite directions.
The little frame that carries the springs screws on to the
crutch in the same way as a common adjustable fork.

DIAL WOKK.

149. In turret clocks the dials and dial work aie ge-
nerally at some distance firom the clock. The dial work
consists of an arbor which carries the long hand with a
wheel upon it, and upon this arbor is the short hand socket
with its wheel, and the two work together in the way
before described in house clocks. These wheels are all set
in a small separate frame fixed behind the dial, and all the
wheds and arbors should be made of brass, as it is gene-
rally not very easy to get at the dial work to oil it ; and
so if made of steel the pinions are liable to rust. The

LEADING OFF. 191

hour arbor projects througli the front of this frame^ with a
half universal joint, and if it is on the same level as the
clock, it is merely connected with the hour wheel of the
clock by a straight rod. If the dial work is above the
clock it must be connected by bevelled wheels, one pair at
the clock and the other pair at the dial work, or, if there
are more dials than one, at some convenient point where
the rods converge from the dial work of each dial, acoasding
to the position of the clock. These vertical and horizon-
tal leading-off rods are sometimes made of tubing, either
iron or brass, as it is stronger than a solid rod of the same
weight and strong enough to resist bending by its own
weight as well as twisting. In the same way I may
mention that small iron gas-pipes with solid pivots fixed
into their ends are sometimes used when cranks with long
arbors are required for connecting the hammer with the
wire coming up from the dock. But where the vertical
rod is required to be long and consequently heavy, it is
generally better to make a wheel at the top of it rest on
friction rollers, and then the weight of the rod has no ten-
dency to bend it, and it only requires to be strong enough
not to twist, for which a half inch iron rod is sufficient in
almost any case. These friction rollers may be made in
various ways ; on the whole the best way appears to be the
following, which will be readily understood from the
drawing over the page.

The rod has a circular plate fixed to its top, and there
is a similar plate fixed to the beam through which the rod
passes. These plates are not quite flat, but they each have
a broad circular groove in them near their edge and the

192 TCRRET CLOCKS.

grooves exactly face each other.
Now if tliree or four equal balls
or cheese-shaped rollers were laid
on the groove in the tower plate,
and the upper platelet down upon
them, it would turn with no fric-
tion except that of the roUinff of
the balls, which would alwajri
keep their original distance. The revolving roof of the
building which contains the great telescope at Cambridge
tarns upon cannon balls in this way ; and the balls run-
ning in the grooves cause it always to turn on the same
imaginary axis without the necessity of a real one. How-
ever on this small scale, in order to prevent the balls from
shpping uid so getting all together, they are set upon a
three legged axis with a hole in the middle which surrounds
Uie rod ; but it has nothing to do as an axis : that is, it
curies no weight and has no contact with the rod, and
has merely to prevent any of the balls from not rolling on
in case the upper plate should for a moment be lifted off
that baU. Consequently the friction (so far as regards the
weight of the rod work) is true rolling friction, which is
much less than the friction of friction v>heelt of any mode-
rat« size carrying the weight upon their axes. I under-
stand that rollers of this kind have been applied to huge
weather-cocks with long rods to work a dial within a
building, and tried with heavy additional weights without
producing any material difference in their freedom of action.
It should be observed that the cross section of the rollers
must be of higher corvatnre than that of the grooves, so

LEADING-OFF WORK. 193

that they may only have contact at one point, and not nib
as well as roll : complete surface contact without rubbing
could only be obtained by conical rollers between conical
plates, the points of all the cones converging in the centre of
the rod ; but such rollers would have a tendency to slip
outwards, and would require greater accuracy in making
than these ' cheese shaped' rollers.

The long vertical rod is connected with the arbor of the
bevelled wheel in the clock by means of a half universal
joint; and in fixing it in cold weather it should be remem-
bered that an iron rod thirty feet long will become ^th of
an inch longer with 40^ of additional heat, and brass tubes
about half as much more ; and play enough must be left
in the joint accordingly.

Where the clock does not stand in the middle of the
chamber, under the point of convergence of the dial rod?,
but near the wall, an additional pair of bevelled wheels is
required. This might be avoided by making bevelle4
wheels of a different angle from 45^, so as to lead directly
to the two side dials from the place where the vertical rod
comes up ; but nothing material either in expense or fric-
tion would be saved thereby. The bevelled wheels, espe-
cially those which have to work several others, ought to be
large and strong; and when, as sometimes happens, their
diameter is limited by want of room in the clock, it ought
to be made up in thickness, which however gives more
friction than krger wheels with more teeth.

ADJUSTING WOEK.
The adjusting work, for setting the hands when the

194 TUEAST CLOCKS.

clock wants altering, is sometisEies very defectiye. I have
seen a clock in a cathedral put up only a few years ago,
as I was told, by a London firm of large business, in which
the only means of putting the clock forward is by taking
oat the bush of one of the wheels (which is famished with
hand-screws for the purpose) and shifting the place of the
pinion upon the teeth of the next wheel. I should think
the man who has the charge of such a clock takes very
good care always to keep it on the gaining side, as he can
stop it for a few minutes every now and then with in-
finitely less trouble than he can put it forward in this
barbarous fashion; The adjustment is generally made
merely by a friction spring as in a house-clock (73). And
where there is only one small dial this method is safe
enough ; but otherwise the spring must either be so strong
that the hands cannot be altered without applying great
force to the wheeb, or else they will be liable to slip for
want of sufficient friction or pressure of the spring. In
large clocks therefore a better way of making the adjust-
ment is by what may be called a square ratchett, i.e, one
which wants the click lifting by hand to enable it to pass
either way, each division corresponding exactly to one or
two minutes ; or by clamping screws.

When there is no hour wheel in the train this ratchett
is sometimes set on the great wheel arbor, turning in three
hours suppose, and with a large bevelled wheel attached to
it, which drives the first leading off bevelled wheel, of one
third its size and number of teeth. This has one advantage,
yiz : that the friction of a subsidiary hour-wheel is
avoided ; which however is much less than if it were an

ADJUSTING WORK. 19{>

additional wheel and pinion in the train : the large bevelled
wheel also carries three pins instead of one, to let off the
striking part* But it has several disadvantages : first, the
small bevelled wheel is necessarily of small dimensions;
since even the large one, which is three times the size,
must be made smaller that the great wheel itself, or it
could not be got into the frame : secondly, the discharge
ing pins cannot be relied on to let off the striking part
correctly within several seconds in this way : thirdly, when
the leading off is wanted in any but a vertical direc*
tion, the arrangement becomes clumsy and inconvenient ;
fourthly, the ratchett-wheel, bevelled wheel, and pins add
nearly two inches to the length of all the arbors; and
fifthly, in some positions of the wheel the adjusting click
cannot be got hold of without great difficulty. I think
any of the following methods are better, and some of them
may be easily adopted in any clock, according to circum*
stances.

When the hour-wheel is not in ihe train it is to be a
thick wheel of the proper size to be driven by the great
wheel according to its velocity. It is not fixed to its arbor,
but rides upon it close to a plain or blank wheel, which is
fixed to the arbor, as are the discharging snail and the first
leading off wheel, if any are required. If the dial is a small
one the hour-wheel and the blank-wheel may be connected
by a friction spring as usual ; otherwise the connection may
be made, either by one or two clamping screws, or by a pin
which goes through a hole in the hour-wheel and into any one
of sixty or thirty holes in the blank wheel, being kept in its
place by a spring, and having a projecting handle by which

196 CHURCH CLOCKS.

it can be pulled out and the relative position of the two
wheels shifted through a space corresponding to one or two
minutes. Another waj^ perhaps still more simple, of
making the adjustment by a definite quantity, would be to
make the hour-wheel^ instead of riding or turning on its
arbor^ to slide upon it by means of a square^ or what is
called a hey; when you want to alter the clock you would
only have to slide the hour-wheel out of gear with the
great wheel and slide it in again with different teeth in
contact^ and it might be kept in its place either by a pin
or a spiral spring of wire round the arbor. Where the
clock has a train remontoire, which may itself require
adjusting^ as described in § 177, clamping screws must be
used ; because altering the remontoire- by any less quantity
than the twenty or thirty seconds at which it lets off would
make the hands point wrongs if they could not be altered
by as small a quantity as the scape-wheel. Where either
of the other methods is adopted^ so that the hands cannot
be altered by less than a minute^ the smaller adjustments
must be made by stopping the scape- wheel for the requisite
number of seconds ; and on this point I shall have to make
some farther remarks in § 187.

SIZE OP DIALS.

151. The size and strength required for the going part
of a clock depends entirely upon the number^ size, and
situation of the dials ; though there seems to be a notion
among clockmakers that the going part and the striking
part ought to correspond in size^ and I have seen a dock
without any dials^ in which the going train was heavy

DIALS. 197

enough to work four dials 10 feet wide. They ought to
be treated quite distinctly; though of course it will fre-
quently happen that where there are large dials there will
be a large bell also. The more turns in the week the great
wheel makes^ the less strength and size it obviously re-
quires ; and in all cases broadness of the teeth^ i. e. thickness
of the wheels^ should be looked to rather than depth of the
rim, as broad teeth cut the pinions less than narrow ones.

The size of the intended clock dials is a matter which
church architects frequently pay no attention to until it is
too late, or do not understand. Mr. Yulliamy states in his
pamphlet the sizes of several well known pubUc dials in
London :

St. MartinVin-the-Fields - - - 8 ft.

St. James's, Piccadilly ... 10 ft.

Islington church - - - - 9 ffc.

The clock on the Queen's Stables - 6 ffc. 10 in.

St. Paul's 17 ft.

Horse Guards - - - - • 7 ft. 5 in.
To which I add from other information :

DIAMETER. HEIGHT.

St. Luke's, Chelsea* - 6 ffc. 10 in. 72 ffc.

Bow Church - - - 9 ft. 70 ffc.

Marylebone Church - 7 ft. about 60 ffc.

Koyal Exchange - - 9 ffc. 90 ffc.

* As a proof of the reliance to be placed on architects in these
matters, 1 have seen a letter from an architect of some reputation,
stating as a justification for the dials which he had prepared, and
which the clockmaker objecte4 to, that the first two dials in this list,
and that of the Horse Guards, were only 5^ feet in diameter : which
his employers had of course believed.

198 CHURCH CLOCKS.

And the great clock at Westminster is intended to have dials
23 feet wide, at the height of about 220 feet.

The result evidently is, that unless all the above
dials are too large, which anybody may see they are not,
dials ought to be so placed that they can be about a
foot in ^idth for every ten feet from the ground; though
tliis is not sufficient for heights under 50 feet. Any one
who looks at dials of less than this proportion, such as
St. Pancras, 6 ft. 6 in. at a height of about 100 ft., or the
dial on the church in Chester Square, which is a little more
than 4 feet, and at a very moderate height, will see a fur-
ther proof of the necessity, not only of making the dials
large enough according to the above rule, but of placing
them where they can be made large enough for their own
height, without being too large for the surrounding parts
of the building. The consequence of not attending to
this is that the tower is defaced, and its ^ details^ over-
whelmed, by what appears at a Httle distance only a great
black spot, too large for the building and too small for the
clock. It is hopeless to make a clock face an archi-
tectural ornament : at least every attempt that I have seen
of that sort in a gothic building ha« Jn a most wretched
failure, both in architectural beauty and horological dis-
tinctness. The best thing that can be done is to put the
dials on some plain flat surface large enough for the pur-
pose; and if such a place is not provided at first, it is ten
to one that a clock-face will some day be substituted for
the tracery of a window (as three illuminated dials have
been in the heads of the windows of the fine tower of St.
Mar/s at Beverley), or buUt round the bottom of the

DIALS. 199

spire^ projecting ' like the eyes of a great cod-fisb/ as I
heard remarked by a spectator of three dials stuck round
the spire of a small country church by the architect just
now alluded to.

152. The material of the dial may be stone^ slate^
copper^ or iron. If the dial is made of stone it should
have the part within the figures, in which the short hand
traverses, cut out or countersunk to the depth of an inch
and a half, in order that the long hand may lie closer to
the figures, for the sake of avoiding pa/rallax as much as
possible. The efiect of parallax is that when the hand is
in any position except nearly vertical, the line of vision
from the eye of the spectator to the hand of the clock does
not fall on the place to which the hand is really pointing,
but somewhere above it, depending on the distance of the
hand from the face and of the height of the clock above
the spectator. The same may be done with slate dials;
but they are more expensive to cut than stone. Stone
dials should be painted all over, black for gilt hands, or
white for black hands, like one of the Horse Guards dials.
Slate may also be painted, though it will keep a tolerably
dark colour without painting, especially if it be occasionally
oiled. Por large dials the slate will have to be in two
pieces. The figures and minute marks are better cut than
merely painted and gilt on the flat surface, as their place
is then fixed once for all : otherwise they are not unlikely
to be incorrectly divided in subsequent painting* In
copper dials this cannot be done, nor the countersinking of
the middle of the dial, without great additional expense ;
and the dial is also obliged to be made convex in order to

200 CHURCH CLOCKS.

preserve its shape: the convexitj should however be as
little as possible^ as it either increases the parallax or re-
quires the long hand to be bent to come nearer the minute
marks^ which has a bad appearance : an inch in 5 feet seems
to be enough convexity.

I am not aware that there is any objection to cast-iron
dials, provided they are kept weU painted; and they are
cheaper than copper. They have also the advantage of re-
quiring no convexity, and the centre can be cast counter-
sunk. I have seen the figures and minute marks made pro-
jecting, which however does not look weU, and is objection-
able, as the hand may be blown against them. They are better
countersunk a little, for the reason I gave just now; and I
may observe that the countersinking should not be square,
so as to leave comers in which the wet will lodge, but a
curved hollow like the fluting of a pillar. Bound dials
always look better than square ones with the spandrils
filled up with some attempt at decoration : a dial is from
its nature necessarily a round thing, and it has no busi-
ness to pretend to be a square one; even arches set in
square heads only belong to the worst style of gothic archi-
tecture, and round windows belong to the best style. But
dials should not be set deep in the wall, like windows, or
the rain will not wash them.

ILLUMINATED DLiLS.

153. Illuminated dials are made of an iron &ame work
or skeleton, in the form of a ring, consisting of the figures
and minutes and the three rims which bound them. The

DIALS. 201

middle of the dial must be one piece of ground plate glas9,
for any division in it would cast a shadow and be mistaken
for the hands. Glass is also put behiud or between the
figures. Several gas-burners are put behind the dial^ and
the cocks of the burners are connected by levers with the
dial work^ so that the clock itself turns the gas nearly off
(but not so far as to put it out) when the day dawns^ and
turns it full on when it becomes dark. This is adapted to
the different lengths of the day by pins which are screwed
in from time to time by the person who has the care of the
clock ; though of course by the addition of more compli-
cated machinery the regulation of the 'gas-movement' fot
the length of the day might be made self-acting.

Another way of illuminatiug a dial^ and a much better
one^ when the building admits of it^ is that which is used
for the Horse Guards clock; on which a strong light is
thrown from a lamp^ with a reflector^ placed on the pro-
jecting roof in front of the clock tower.

SIZE OF PIGUEES.

154. In nearly all public dials the figures are made too
large; for the larger they are, the more they contract the
really useful part of the dial; it will be seen that in most
public dials the figures nearly touch each at their inner
circumference; and consequently that part of the long
hand which is over the figures cannot be distinguished at
all at a moderate distance, and the dial might as well be
only two-thirds of its actual size. Nobody wants to read
the figures ; twelve large spots would do just as well,— and

^02 TUREW CLOCKS.

better; for then the long hand could be more dearly seen
between them. The figures ought not in any case to
be larger than a quarter of the radius of the dial; and
they ought to be rather narrow^ or their different strokes
close together^ so as to keep the VII and YIII and the
other wide %ures visibly apart from each other. It may
be as well to inform those who have not seen it tried^
that it has a bad effect to make the figures narrower at
their inner circumference than at the outer^ as if the strokes
were formed by radii of the dial ; and this is a further
reason why the figures should be small. The five-minute
marks should be a good deal larger than the other minate
marks^ or it is not easy to distinguish which minute belongs
to the figures that consist of several strokes.

155. Both the hands should be broad; and the short

hand only should have a heart or a broad part a little way
from its pointy and the point of it ought to be entirely
within the figures, and not haH covering them as it some-
times does : the long hand should be straight, plain, and
ending in a point, like a straight sword, just half way
over the minute marks. These directions may seem need-
lessly particular ; but the object of clock faces is to show
the time distinctly as far as possible; and any one who
will compare the few in which these things are attended to
with the many in which they are not (indeed I hardly
know any in which they are all attended to) will see that
the attention is not thrown away; and as it costs no more
to make the figures and hands in this way than in the com-
mon way, there is no excuse for not doing it, unless some
other way really better can be found. The material of the

HANDS. 208

hands is almost always copper^ gilt^ and stiffened at the
back for some distance with a rib of brass. Ironwonldbe
lighter for the same strength^ and when zinced or ^gal-
vanized^ before gilding there appears to be no reason why
it should not answer as well as copper : indeed it is pro-
posed to make the hands for the great Westminster clock
in this way.

156. There is some difference of opinion whether the
hands should be counterpoised externally or internally ;
for one or the other they must be on account of their great
weight. If they are counterpoised internally^ the force of
the wind is not counterpoised at all, and it tends to bend
the hand and drive it against the dial, or, if the hand is
strong enough to resist that, to bend the arbor which
carries it; whereas if it is counterpoised outside, the pres-
sure of the wind against one arm of the lever is balanced
by that against the other, and there is no lateral pressure
on the arbor. And in like manner when the wind tends to
htm the hand in one direction it will tend to turn the
counterpoise in the other direction, and so there will be no
strain on the teeth of the wheels, which in large dials, with
the leading off or dial wheels not strong enough, has been
known to break them. The objection to an external coun-
terpoise for the long hand is that if it is gilt it will be
mistaken for one of the hands, and if it is black like the
£ace it will partially hide the hour-hand for about twx)
minutes in every hour. My own opinion is, though it is
contrary to the modem practice (which has perhaps been
adopted by clockmakers to guard against the propensity of
painters and gilders to gild the counterpoise), that the

204 TURRET CLOCKS.

partial hiding of the short-hand for a minute or two is of
far less consequence than the pressure upon the arbors and
upon the train of the clocks which is caused by the want
of an external counterpoise^ whenever there is a high wind ;
and I should accordingly (especially where the dial is high
and large) have a black external counterpoise to the long
hand^ with its broad part (which it requires to make up
for the want of length) falling just within the inner rim of
the figures^ and therefore just beyond the heart of the
short-hand. The black counterpoise of the short-hand will
of course cover nothing but the black face. There ought
however to be set on each of the dial rods inside^ a longish
arm in the same way as an internal connterpoise, to enable
a person fixing the dial work to know the position of the
hands outside. It is not uncommon to see tliree or four
dials on a tower all showing different time^ or to hear the
clock strike when the minute-hand is not pointing to
the 60th minute. When internal counterpoises are used,
the arms which carry them should be as long as the space
will allow, because the shorter the arm is which carries the
weight the heavier the weight must be, and the greater the
constant pressure on the arbors and sockets.

MAINTAINING POWER FOR WINDING UP.

157. As turret clocks take longer time to wind up than
house clocks, they still more require some maintaining
power to keep them going during that time. In the best
clocks Harrison's going ratchett (7^) is used; but care
must be taken that the spring has play enough to keep the

BOLT AND SHUTTER. 205

tram going with proper force the whole time of winding.
In clocks of moderate size the spring may very con-
veniently be made merely of steel wire^ wrapped in coils
with about }th of an inch interval between them^ round a
lod bent into in a circular arc^ of which one end is fixed
to a spoke of the great wheel and the other end runs
through a socket screwed to a spoke of the ratchett wheel,
so that the spiral spring is compressed between the two,
being kept in its place by the circular rod run through it.
In very large clocks however it is difficult to get force
eEOUgh with springs of this kind, and therefore they must
be of the shape drawn in § 72; and in all cases there
should be two springs on opposite spokes, both for greater
security and because you can get more play with two than
with one of twice the strength.

158. But there is a more common and much cheaper
kind of maintaining power for turret clocks, which goes by
the name of the boU<md ahuUer; in which a weight at the
end of a lever is made to drive one of the wheels in the
train for a few minutes. The drawing at p. 209, though it
is not intended to represent the common construction, wiU
serve to explain it. The lever A £ D carrying a weight
at its end turns on an arbor A, and at B there is a bolt or
click (shown as a fixed bolt in the drawing), which wiU
allow the lever to be raised, but not to fall again without
turning the great wheel with it. This bolt is more com-
monly made to slide in a socket, like the spring bolt of a
door; but this is a bad plan, as it is very liable to stick,
and then the clock is left without any maintaimng power.
On the long arm of the lever there is placed a cap or

206 TUEEST CLOCKS.

shutter (different from that shown in the drawing) which
covers the winding square C when the lever is down or not
in action ; and therefore the man has to raise the lever and
shutter out of the way^ before he can put the winder on.
The bolt is generally made to act on the centre wheel be-
cause that requires a less weight ; but where the dial work is
driven independently by the great wheels as in § 150^ this
is objectionable^ because it causes the centre wheel pinion
to act backwards : if it is inconvenient to apply it to the
great wheel it would in this case be better to apply it to
the hour-wheel which is driven by the great wheel. And
in any case it is to be remembered that the maintaining
power only acts until it has run the bolt out of gear^ and
drops on to the stop G, or some convenient part of the
clock &ame^ and it will of course run itself sooner out of
a wheel that turns in an hour^ and stiU more out of one
that turns in about twenty minutes, than it will out of the
great wheel. It might indeed be made to act longer by
setting the lever upon an arbor concentric with that of the
wheel or nearly so, and making the dick throw itself out
by coming against a pin in the frame when it had got low
enough; but the more simple and safer way is to make it
act on the great wheel as the dock weight does.

But the great defect of all the common methods of
constructing the bolt and shutter is that you have no se-
curity for the lever being raised far enough to keep it in
action during the whole time of windiQg up, especially if
the man loiters over it, as he is very likely to do in winding
a large dock with a heavy weight. There is also a smaller
defect of just the opposite kind, viz : that the maintaining

BOLT OR SHUTTEK. 207

power generally remains in action for some time after the
winding is done^ and so there is a double force on the
clock. This does not happen with a spring going barrel;
and though that may also theoretically run itself down if
the man is too long winding, yet practically it can hardly
happen, because if he stops to rest he will of course let
the weight go oflf his own hands on to the clock, which
win at once restore the tension of the spring, and he will
begin winding again with the same maintaining power as
at first. Indeed in a clock that takes several minutes to
wind and has a spring going barrel, it is better to direct
the man always to stop and leave hold of the winder in
the middle of the winding.

But, on the other hand, it is impossible to make the
spring act with equal force during the whole time. In
clocks of the common construction this is of very Httle
consequence, for the spring is only required just to keep
the scape-wheel going, as a heavy pendulum wiU go for
many minutes without any sensible variation, even if it
receives no impulse at all &om the scape-wheel. But in a
dock with a remontoire in the train, which always requires
a certain amount of force to Uft or wind it up, it is evident,
that if the spring is to be strong enough to do it when it
is nearly run down, it must act much more strongly than
is necessary at first; and the larger the clock, or the longer
it takes to wind up, the greater must be the excess of force
to be left constantly on the clock train, in order to bring
the spring to the requisite tension; which, though it will
not reach the escapement, being intercepted by the remon-
toire, is of course a defect, and helps to wear out the dock;

208 TURRET CLOCKS.

and therefore the spring-going barrel is not so well adapted
for a remontoire clock as some kind of maintaining power
which acts by gravity, and so is pretty nearly constant.
Mr. Airfs going-barrel, which will be described in § 160
effects this object; but it so enormously increases the ex-
pense and trouble of making the dock, and is so unfit tp
leave in the hands of any but skilful persons afterwards,
that it is impossible that it can ever be generally used. I
have therefore attempted to contrive an improved bolt and
shutter, which shall be capable of acting for a much longer
time than can possibly be required for winding, and yet
can be thrown out of gear as soon as the winding is done
(which the common bolt and shutter cannot, without open-
ing the dock-case), with a provision to secure its being so
thrown out; and which will also have the more important
advantage of rendering it absolutely impossible to begin
winding without previously raising the lever to the fall
height it is intended to go. All this can be done by a
very simple addition to the common bolt and shutter, and
in a manner which supersedes the necessity for any sliding
bolt or click.

159. The bolt B is now, as it appears in the drawings
merely a fixed tooth on a short arm of the lever, and it is
put into or out of gear with the great wheel, by sliding the
arbor A backwards or forwards in its pivot holes. The
shutter CE is no longer a cap covering the winding square
when it is down, but a circular arc, whose centre is A«
and which comes dose up to the winding square, so that
when the arbor A is pulled forwards, or out of gear with
the whed, you cannot get the key or winder on. And

NEW BOLT AND SHUTTER.

in order to prevent the lever from being merely pushed
back, without being properly raised, its end D, or another
arm projecting from it in any convenient place, rests, when
the lever is out of gear, in front of the stop F (which will
be further described presently), so that brfore you can push
the lever back, you must lift it over the top of P, and then
push it back, and so into gear; i^r that you can piit the
irinder on, and as the clock goes on the lever falls, and the
end of it descends behind the stop F, aa shewn in the side
view of /P Q. Now F/is a kind of flap or valve turning
on a hinge at/; and it will be seen, on looking at the side
view of it, that you can, when you have done winding, pull
the lever D forward, with its arbor, which will pull the flap
forward ; and then the bolt being out of gear, you will let
the lever drop in front of F on to the block G below it, and
the flap immediately falls hack, so that you cannot get the
lever back again by the way it came out, but it must go over
the top of F, as at first, when you want to wind up again.

wo TUBRET CLOCKS.

The reacter may be inquiriiig, what will happen if tiie
man omits to pull the lever out of gear : the clock mil atop
in five or ten minutes^ as the lever will hold it fast. This
is so done on purpose^ for it might be very easily avoided
by making the bolt a clicks as before; but then you
would have no security for the lever being properly thrown
out of gear when the winding is done^ and being left in
such a position that the man cannot begin winding the
next time without raising it. I had originally designed it
with a self-acting inclined plane behind F, to throw the
lever out of gear as it descends ; but, on the whole, I am
satisfied that it is better to omit that provision, as it would
encourage carelessness in the man who winds; for he would
probably never take the trouble to pull the lever out of
gear, if he knew it would do so itself in a few minutes,
and consequently he would always leave the clock with tiie
double force on ; which he would take care not to do if he
knew the clock would immediately report his negligence by
stopping. It is obvious that this apparatus can be appHed
as easily to any other wheel as the great wheel, though, for
the reasons I have mentioned, I prefer that wheel. Where
the going part winds up by a jack- wheel, as I have recom-
mended (141) for large clocks, even when not absolutely
necessary, the shutter C D might be put merely behind that
whed, so as to prevent it being pushed back without first
raising the lever; and then pulling the lever out of gear
would, at the same time, throw out the jack-wheel, and is
no more trouble than doing that alone, as is done in the
apparatus which I must now describe.

MR. M^S GOING-BARSEL.

160. This mamtaiiimg power vas originally inveiitod
for the great eqnatoreal'telescope-driving clock at Gam-
bridgCj which lias a revolvii^ pendalum (16), and there-
fore wiU not bear even the momentary disturbance of putting
on and taking off an ordinary bolt and shatter, though l^e
force is very nearly uniform when it is on. It is applied to
the Exchange clock, and is intended by Kr. Aiiy to be ap-
plied to the great clock at Westminster.

The constructioii r
of it is curious, and
will require some
attention to nnd^-
stand the principle
of its action. The
barrel arbor C is not
set in the clock
&ame, bat in a
swinging frame, of
which one side is
CAD, and which

tuma on pivots of ite own (not an arbor going through
the frame) at A, and is kept balanced between the wdg^t
M whicb is bong to it aa shown in the drawing, and the dock
weightWwith the weight of the barrel and ita wheels, as fol-
lows. The pivots A are so placed that C A = the radius of
the barrel. The reason why the sides of the frame are not
straight will be explained afterwards : fj is the point where

212 TURRET CLOCKS.

H would bang^ if the sides were straight, or where C A
produced meets M D produced. At B is the pinion of the
centre wheel. Now, since the dock weight W hangs hj a
line passing through A, we may suppose the whole as a rigid
system (there being a proper contrivance to make it do so)
to turn round A for a short time, and we shall then have

M Y^ as the force of M upon the pinion B ; but this is

diminished by the weight of the* barrel and its wheels,

which we may call N; and their centre of gravity being C,

C A
they will produce a force on B the other way = N -r-^. If

therefore we suppose for convenience A ^2 to be made = A C,

the force upon B when the system all turns round , A will

AC
be (M— N)t^. And we want this to be equal to the

force exerted by the weight W when the barrel and

. < • A C

wheel turn round C as the fixed point, which is Wg-g:

therefore, in order to find what the weight M must be, we
have the equation 7^ =bc '• M=N+Wg-g.

Suppose, for example, that N = 1 cwt., W= 2 cwt,,
and the diameter of the barrel is half that of the wheel,

org-Q=|' then M will have to be 4 cwt. The way in

which the machine is all made to turn round A while wind-
ing up, or while the weight W is taken off the clock, is
this : there is a click K fixed to the frame C A D at A, and
working in an internal ratchett of the great wheel, of which
a few teeth are shown in the drawing; the common barrel
ratchett H being fixed to the great wheel.

The clock is wound up by a jack wheel G, working into
a wheel set on the end of the barrel as in other large clocks;

HB. aiet's ooing-babrel. 213

the jack wheel arbor is placed on a level with C A, and
therefore the point of contact A of the two wheeb may be
considered a iBxed pointy and the whole system is still
balanced upon it while winding. The arm AD is made
oblique^ in order that if the equilibrium between M and W
should be deranged by the friction of the pulleys or other
causes, it may speedily restore itself^ a small motion of the
point D causing a sufficiently large alteration of the length
oi kd, or of the moment of M. Aeii^; whereas if GAD were a
straight line, this moment would not be sufficiently changed
until the frame had moved through a large angle, and pro-
bably ran itself out of gear altogether. It will now be
easily understood that this machine must be exceedingly
expensive and troublesome to make and fix ; though the
mere elevation or section of it in this drawing gives no idea
of the additions and alterations which it renders necessary
in the clock frame and the rest of the train. And after all,
however useful it may be for a dock with a revolving pen-
dulijun, it does no more for a dock with a vibrating pendu-
lum, and especiaUy one with a remontoire, than a common
bolt and shutter, which does not cost one fiftieth part as
much as this did in the Exchange dock, provided only you
can make sure of its being properly applied; which, as
I have shown, may be done very easily and cheaply.

STKIKING PART.

161. The striking part of a church clock is much the
same as that of a house dock, except in the position of the
hanmier, and its. acting by its own weight instead by a

TDEBET CLOCKS.

spring. The shape of lu^ bells beu^ not hemispherical, bat
of the shape in this drawing, the thick part S or sotmd bow

of the bell is so carved, that a tangent to it wonld make an
angle of about 35° with a horizontd plane : and therefore
the axis C of the hammer mnst be so placed that G S will
form that angle with the horizon. As in house clocks the
hammer is prevented from jarring on the bell by a spring as
shown in the drawing.

Now it is evident that a hammer resting in this position,
and rising in a circular arc, requires more force to raise it
at the beginning than at the end of its motion. But as
striking pins of the common construction must begin to act
at some distance from the end of the lever which th^ raise,
their force is leta at the beginning than the end of the
motion, and so a good deal of the force of the clock is
wasted, and the hammer is not raised nearly so high as it
might be if the action were unifonn. As reg&<^<) the ham-

STRIKING PART. 215

met, we may remove this inequality in a great degree by
putting it on a long shank^ as it will then rise a given
height with less angular or circular motion^ and con-
sequently with less waste of power in the train which raises
it^ and it will also fall with less Motion on its pivots^ and
therefore greater velocity. And as regards the striking
pins^ we must make them of such a shape that they do not
begin to act at some distance from^ but at the end of ^the
lever : that is to say, they must be of the form called co^s
or canu, of which the curve is to be determined by calcula-
tion or experiment, so that the lever may always act only
upon its end, and with a sliding and not a scraping friction
between the two surfaces.

162. Now raising a lever by cams, or co^s, or wipers, is
a different thing from driving a wheel, though it may
appear to be the same thing; and I may as well warn any
reader of the common translation of 'Camus on the teeth of
wheels,' that the rule for the construction of cams given in
the Introduction (which is not Camus's) is entirely wrong,
from overlooking this difference : it would be right if the
end of the lever were a round pin. In wheels, when a tooth
of the ' driver' has' driven a tooth of the ' follower' to a
certain distance, they leave each other, and the motion is
taken up by another pair of teeth ; aad when the two teeth
part company, the end of the driving tooth is pressing
against the side of the driven one, and not at its end, as the
teeth G, c, in the drawing at p. 138 ; whereas a cam raising
a lever must finish with the point of the cam at the end of
the lever. Therefore the curve of the cam must, firstly, be
such that it will remain acting upon the end of the lever all

216 TURRET CLOCKS.

the time^ instead of begiimiiig at the end^ and then going
£Eurther up, as in a wheels and then sliding back again ; and
secondly^ with a view to diminishing the friction^ the curve
must allow the end of the lever to move upon it as a
tangent through the whole motion; and in that case^ if
the lever wears at all^ it must still wear itself as a tangent,
and will therefore never change its proper form, if the end
of the lever is made a circular arc round the centre on which
it turns.

163. The curve which would do this accurately is called
in mathematical language a tractrix, because of the mode in
which (theoretically speaking) it can be described. Prac*
tically however that method cannot be made to answer;
neither is there any other convenient way of describing
it, as far as I know. But it luckily happens that a curve of
the same nature as that which is required for teeth is sufBi-
ciently accurate for any such angle as a hammer lever has to
move through, though it would not do for large angles."^ It
will be found by any one who makes the calculation, that
there will be no appreciable error, for angles up to about SO^,
if ^ be the length of the levet or tangent, a the radius of the
circle upon which the cams are to be set, and r the radius

* I may remark that this curve does not raise the hammer with
quite uniform velocity, but rather more quickly at the beginning.
The difference however is very small, and is of no consequence ; for
as the train always has a little run before it begins raising the ham-
mer, it has more momentum at first. In fact, a clock made in
the common way will often not be able to start itself, if the wheels
are so placed that the lever is left just reating on a pin when it has
done striking, for want of the momentum acquired by the run previ-
ously to encountering the resistance of the hammer.

STRIKING CAMS. 217

of the cirde which is to generate the epicycloid by rolling
on the circle of rad. a, and r is determined from the equa-
tion, %r=^y/a*-^at—a.

Tor example, suppose ^ = 4 inches, and as = 8, then r
will be *9 inch, or rather less than a quarter of the length
of the lever ; and it will not be much affected by changing
the value of ^ to a moderate extent. These are the sizes of
a and ^ in a large clock which Mr. Dent has lately made for
Tavistock church, in whic^h this construction was adopted.
There are 24 cams on the wheel of the hour part, and 36
on each side of the great wheel for the quarters. The hour
bell weighs 80 cwt. ; and though the wheel with these
cams on it is of cast iron, and their surfaces are not polished
as pins always are, the striking weight is only 2 cwt., with
a fall of about 60 feet, which every dockmaker will recog-
nize asi< much less than usual for eight^day clopks striking
on much smaller bells. This arises partly from the shape
of the Cams, and the short run of the lever upon them, and
partly from their being on the great wheel instead of the
second wheel, and in some degree also from the cams acting
on the lever on the same side of its axis as the hammer
wire, being what is called a lever of the third order; for
in that case the pressure on the axis, which produces the
friction, is only the difference between the pressure caused
by the weight of the hammer, and that of the cams, instead
of being the 9um of those pressures, as it is when the clock
and the hammer are both pulling upwards at opposite ends
of the lever.

164. The striking part of the Tavistock clock; that is,
tiie same patterns of the wheels, is adopted also in the Mean-

213 TCEEET clocks;

wood dock, vhich luu a bell of only 1 1 cvt. It msj be
•Imposed that the same trheel cannot be right for a bell of
11 cwt. and one of 30 cwt. F^haps if it had been neoes*
■ai7 to malce a new patteni, it might haye been made of
15 inches diuneter instead of 18, but certainly not lessj <»■
■ it woold have made the spaces for the cams inconvenieEtly
■mall. And the extra size and weight are of no conse-
qoeuce in the first wheel of the train, especially as the rope
polls upwards. The result is that by adopting this ar-
rangement of the cama and a cast iron wheel, one pattern
will serve to produce wheeb £t for a bell of 11 cwt., and
also a great deal stronger than the old-^sMoned whed
which raiaes the hammer of great Tom of Lincoln. As I
believe this kind of wheel is new I have given a sepaiate
drawii^ of it, shoning a few of the cams, and the lever.

But although the exact value of a in the above equation
ia immaterial for the purpose of determining the shape of the

NEW STEIKING WHEEL. 219

^picycloidal cams, we have still to find out at what depth
the cams must be placed, so that their points may just come
up to the bottom of the teeth of the wheel, which must be the
boundaiy of the cams. For this purpose cut out in tin or
paper a pattern of one of the cams of greater length than
will be required^ and also cut on the tin an edge represent-
ing a tangent from the bottom of the cam, which will be a
radius of the great wheel, and prolong it to a point T at
the distance i from the bottom of the cam ; and cut out
also on the same piece of tin an arc of the circle which
will be described by the lever # round T (leaving a piece
of the tin at the junction of the cam and of the arc suffi-
dent to hold it together). Then draw on a board a circle
about ith of an inch larger than the bounding circle and
divide it according to the number of the cams. Take the
tin pattern and slide it about on the board, takiag care
always to keep the edffe which represents the radius of the
wheel iu a rail posiL, untfl you see that a portion of
the cam and of the lever-arc is just iucluded in one di-
vision of the large circle.

The place where the point T falls on the board will then
give the exact distance of the centre of the lever arbor
from the centre of the wheel : and another circle drawn
on the board of the exact size of the bounding circle will
cut the points of the cams at the proper place ; and their
bax5ks should he cut away in circular arcs drawn with a
radius a little longer than t. The reason why the first
circle was drawn on the board rather larger than the actual
bounding circle was to allow the lever to fall off one cam

a little b^ore the next is ready to receive it. And it must

L 2

220 TURRET CLOCKS.

be remembered that the length of the lever must not be
altered from the length t, nor the position of its centre
altered from that determined as above ; and the face of the
lever must be in the straight line or plane joining the
centres of the wheel arbor and the lever arbor. If anj
more space is required to clear the lever in its fall, it most
be taken off the back of the cams and not off the end of
the lever, as it is very tempting to do, or they will no
longer work together without scraping; in fact the lever
had better be too long than too short; and the end of the
lever should be an arc of a circle described round the cen-
tre of its arbor, as it will then always keep the same length
as it wears.

Even if epicycloidal cams are not used, neither small
pins nor rollers should be used ; but the pins should be
cylinders large enough for their action to begin as
near the end of the lever as may be, and half the cy-
linder should be cut away (as indeed every letting-off pin
should be) to let the lever drop suddenly as soon as it
has reached its highest point; which rollers prevent,
causing the drdp to begin slowly, whereby part of the rise,
and the power of the clock, is wasted. The acting face of
the lever should be not less than half an inch broad for a
large clock, for the same reason that broad teeth are better
than narrow ones ; a narrow lever cuts nicks in aU the pins
in a very short time. And in order to take as much pres-
sure as possible off the pivots of the arbor on which the
lever is fixed, the two arms' of the lever should be as close
t(^ether as they can be placed ^nd not one at one end of
the arbor and the other at the other ; and all the cranks, if

FORCE LOST IN STRIKING. 221

a^y are required, should have long arms, in order to di-
mLh the angulL motion requiri for a given ™e of th.
hauuner ; and there should be as few cranks as possible. .
165. I have described a simple method (20) of trying
what force any given escapement is really using, or how
much of the going weight is employed in merely overcoming
the friction of the train. It may be ascertained by a
»till more simple method, how much of the striking weight
is lost by friction, and the motion of the train between
every two blows, and by the hammer lever and cams bei^g
so arranged that nearly all the power is consumed in raising
the hammer the first inch. It appears that the hanmier
shank, or rather the line from t}ie axis to the face of the
hammer,' generally makes an angle of about 35^ with the
horizon. Since we caimot help some force being lost by
the rise taking place in a circular arc instead of a straight
line, though the radius of the arc ought to be made as
large as possible, we may, in comparing one clock with
another, assume the hammer to rise in a straight line at an
angle of 35° to the vertical. Therefore if H ia its weight
(beyond what is required to balance the rod work, strictly
speaking), and d the rise from the bell, the work done by

the hammer in the day is 156 Rd cos 35° ; and if A is the

W h .
actual fall of the clock weight W in « days, — ia the work

it ou^At to do in the -day if no force were lost; and the
ratio of these two quantities will show what proportion of
the power is lost. Cos 35°= '82, and il d is expressed in
inches and A in feet, and n is eight days, the above ratio

will be very nearly , which, if there were no loss of

power, would be a ratio of equality. It wiU be found

222 TURRET CLOCKS.

however that it is seldom as mnch as i^ and often as little
as i^ in docks that strike from the second wheel. In the
Exchange clock it is rather more, because it has cams, not
pins. In a table given of five existing clocks among the
parliamentary papers respecting the Westminster dock, the
t)nly one, even if those that strike from the great wheel,
that gives this ratio as high as | is the one in Wilton
Place (St. Panics, Knightsbridge), which is a clock with
east iron wheels and cams; not Uke the Tavistock whed,
but with ten cams on each side and two hammers raised
alternately. In the Tavistock clock the above ratio is as
high as }; or only ^th of the power of the clock is lost in
fidction and the necessary interval between the hammer
Ming and beginning to rise again.

166. It is mentioned in one of the parliamentary papers
that in some foreign clocks the hammer is placed with its
head downwards and its axis near the top of the bell; so
that it is easier to raise at the beginning than at the end
of the motion. This is no doubt an advantage when the
hammer is raised by pins which begin to act at some dis-<
tance from the end of the lever ; but it must be remembered
that a hamm^ so placed will require a much larger angular
motion than one placed as usual to raise it to the same
vertical height, on which the force of the blow depends, and
not merely on the distance from the bell to which it is
raised; for it will be seen on looking back at the drawing
of a bell that the hammer shank must stand at a mach
larger angle with the horizon than 35** when the hammer head
is downwards, and moreover it wiU strike the proper part
of the bell more obliquely, since the angle of 35** (or

POSITION OF HAMMER. ^23

thereabouts) is adopted just because it is that which enables
the hammer to strike the bell as directly as possible.

When the bell is not required to be swung, the hammer
might indeed be set at the proper angle by putting the
head upon a sort of double shank embracing the bell. But,
as has been shown just now, we can get quite sufficient rise-
out of a hammer set upon a shank of proper length in the
common way, with no greater loss of power than Jth; a
great part of which must, under any construction, be
lost in the necessary interval between the fell of the ham-
mer and its beginning to rise again, and in the inevitable
loss due to the hammer spring; and therefore I think we
may be more profitably employed in improving the construe^
tion of the clock itseH than in making or adopting contrive
ances to meet a defective construction.

. I think however that it is a question worth consider*
ing, for a stationary bell, whether it would not be better to
make it stand with its mouth upwards, that the hammer
may strike it on the inside, as the clapper does. No clock-
hammer ever gets such a sound out of a bell as the clapper
<loes when it is ringing in fiiU swing. It is not impro*
bable that the bell opens under a blow more freely than
it closes : a blow on the inside makes the circle open in
that part for its first vibration, whereas a blow on the out^
side is resisted by the bell as an arch.

I may mention that a stiff hammer-spring, which allows
the hammer to stand very near the bell, is better than a
weaker one, which admits of larger vibrations, and therefore
requires the hammer to be kept farther off. I have much
increased the sound of a house cbck with an unusually

224 TURRET CLOCKS.

lanre bell and hammer, by substitatinff for the common stop-
«pSg a thin piece of v^canized InLrubber, set upon a
firm stop just below the hammer-head. Moreover^ tlie
hammer ought to have a broad face^ and not, as some clock-
makers fancy, a sharp one. Besides the inferiority of the
sound, I remember a very large and fine bell being cracked
by a hammer set so as to strike with its edge* >

, QUAETEES. '

167* When the clock strikes quarters, the striking
wheel is made in the same way as the hour striking wheels
only with cams or pins on both sides of the wheel, of the
proper number for each hammer to strike 120 times in the
twelve hours instead of 78. The cams on one side should
not be set half way between those on the other, but the
cam that raises the second hammer should be behind the
other by about one-third of the distance between two
successive cams on the same side, in order that the interval
between the two blows of each quarter may be half that be*
tween each successive pair of blows. In this case I sup-
pose both the levers to ride upon one arbor, which is a bet*
ter arrangement than putting them on different arbors, one
below the other. In the Tavistock clock, the. two levers
axe arranged as shown in this drawing, in order to bring
both their long arms, into the most advants^eous position.
I have not thought it required to show the moveable
bushes, which are necessary to enable the arbor of the two
levers to be passed through all the four holes in the frame
and levers.

In all cases, both for the hour and quarters, there ought

QUARTRR CHIMES.

to be a atrong stop (if cast on the frame all the better) for
the long arm of the levers to strike against when the ham-
mer falla, to take the ahock off thestriking pins, and, as far
as possible, off the arbor. Such stops are often put to the
short arm, and mnch t«o weak, and too near the arbor.

The quarter bells should be the Ist and the 4th or 5th
of a peel of 8, the hour bell being the 8th. Where there
ate less than 8 bells, quarters may struck at every quarter
except the 4th ; and this will only require 72 blows for
each hammer in the twelve hours.

168. Wherever there is a peal of ten bells, the quarters
may consist of chimes hke the well known chimes of St,
Mary's at Cambridge, or that (in my opinion) very inferior
' improvement' of it at the Royal Exchange, for which,
however, it is right to state that the maker of the clock is
no more responsible than for the bells, about which there
has been so much discussion. The bells used for such
chimes are the 1st, 2nd, 8rd, and 6th of a peal of six,
or (which is the same thing) of a peal of ten, the 10th

286 TVRBET CLOCKS.

feeing the hoor-beU. It cannot be done with a peal of
eight, becanse the first six do not themsdves fonn a peal;
and the 4th of a peal of eight is a very miserable substitute
lor tke 6th of a peal of ten; though it is adopted in some
places^ as at St. Clement's churchy in the Strand ; and I
eonld mention a clock made for a nobleman a few years
ago, who intended to have the Cambridge chimes, but the
five bells had been cast of the notes for a peal of eight
before the clockmaker learned (on asking me to famish
him with the proper changes) that the bells would not
make those chimes at alL To prevent snch mistakes in
future, I will state what the chimes are, both of the Cam-
bridge and Exchange quarters, and the construction of the
barreb to produce them ;

Cambridge* Exchange.

^ , ( 3126 \ 1st - ( 3126 ) \ 2A

1326 1*^*^ (l326 (

8d ] 6213 / 8218 J

{ 1236 - 1st

•

{The Cambridge barrel turns twice in the hour, having only
the five changes set upon it, and the number of them to be
played at each quarter is determined by the locking'plate,
which turns once in the hour. The barrel must first
be divided not into 20 but 25 equal parts, and every fifth
division left without a pin in it, in order to aUow twice as
much time between two successive changes as between two
successive notes of the same change. In the Exchange
chimes, the reader will see that each quarter begins with
the same change, and therefore, though there are only fotir
dianges altogether, yet the barrel must take the whole hour

to iXifxi m> atid most have 40 pins in it^ instead of the 20
required for the Cambridge chimes. And consequentlj,
besides the inferiority in the tunes played by the Exchange
dock to those of St. Mar/s^ you cannot tell what quarter
it is until you have heard out the whole tune; whereas
everybody in Cambridge knows directly a quarter begins
what*it is going to be, except that the hour begins with the
same changes as the half hour.

Chimes of this sort are so much better than the com^
mon ding-dongs, and so much easier to distinguish, at least
when they have a different tune as well as number for
every quarter, that it is to be hoped the present plan of
the great Westminster clock will be altered; and that as
the hour bell is intended to be the largest ever made in
England, viz. 14 tons, so its quarters, if they cannot be
superior to all others in tune as well as size, will be
at least equal to the best 'that are known. Eight bells^
which were proposed by Mr. Barry, are too many for
distinctness as a quarter chime^ and so would cause great
additional expense for no good. Mr» Whitehurst suggested
five; but those a^re very inferior to the Cambridge four.

BELLS.

169. As this subject of bells is materially connected
with that of church clocks, I will add a few remarks upon
it. And first, I may observe that it is sometimes a ques«
tion whether a clock should be made to strike on the tenor
bell of the existing peal^ or upon a little bell to be set
upon the top of the towen When the tenor is a largd

228 TURRET CLOCKS.

bell^ theare can be no doubt that it has much the best effect
to strike on that. But then it generally requires a larger
and more expensive clock ; and unless the tenor is a bell of
at least 10 cwt.^ a small one of two or three cwt. outside
the church will frequently be heard farther^ and accordingly
that plan is sometimes advantageously adopted.

170. Where the bells are not ready made for the 'clock
their size is of course optional; but unfortunately their
quality is not equally at the option of the purchasers. And
in consequence of the disputes which have occurred respect*
ing the Royal Exchange bells^ I wish to suggest to those
who have to give judgment on bells^ that the tune, that is
to say^ the note of one bell relatively to others^ is a totally
distinct thing from the tone, or absolute quality of the bell^
and of infinitely less consequence; because the note can
easily be altered sufficiently^ but the tone of a bad bell can
never be mended^ except by breaking it in pieces^ and melt-
ing it; and not always by that^ if the metal has been bad
originally, or the bell-founder does not know how to make a
good bell. In order to judge of the absolute goodness or
tone of a bell, what is wanted is not so much musical know-
ledge or perception of tune as experimental knowledge of
what bell-metal is capable of. A peal of cast iron bells
might be made perfectly in tune, and to a person who had
never heard bell-metal bells, would appear a perfect peal.
No rules can be given to enable people to judge of the
quality of sounds ; but a few things may be mentioned as
necessary to attend to; such as, whether the bell sounds
freely on being hghHj touched; how long it 'holds the
sound,' compared with other known bells of about the same

BELLS. 229

«2e, and of good quality j and particularly whether on filing
or polishing the bell anywhere the metal appears perfectly
dose and free from holes. If it does not^ you may be sure
the bell is a bad one^ without any further examination^ and
it ought to be condemned at once. A bell may also be too
thin for its size^ and perhaps occasionally they are made
too thick. In bad bells^ it may be frequently observed that
you hear a harsh metallic sound of the knock of the ham-
mer, independently of the continuous or ringing sound,
which alone ought to be heard. Other points must be left
to the discretion of the judge.

As many persons may have read some remarks on the
relative merits of the great bells of St. Paul's and Christ
Church, Oxford, in one of the ParUamentary papers, I must
say that I do not agree with them; on the contrary, I
think St. Paul's far the best of the four large bells of Eng-
land, though it is the smallest of them, being about 5 tons;
while York is 12, Lincoln 6i, and Oxford 7 J, which last
is a remarkably bad bell. There is a general opinion that
bells cannot be made now equal to the old ones. It is true
that bells improve in sound for a few months, but no more;
«nd they only alter in loudness, not in the quality of the
tone. The badness of many modem bells is due not to
want of age, but to want of skill or attention in the founder.
I have seen as bad bells as need be, with dates of about 200
years ago ; and the best I ever heard (for a small peal), at
Castle Camps, in Cambridgeshire, were made about 20
years ago by a country bell-founder, of the name of Dob-
son, who however did not meet with sufficient encourage^'
ment^ and lately died a pensioner in the Charter House;

"SSO TtJEMT CLOCKS.

and many exoellent beUs^ both large and small, Were east
by Mr. Mears, and his predecessors^ Messrs. Leicester^
Pack, and Chapman, at the weU-known foundry in White*
chapd, which for some years has enjoyed nearly a mono*
poly ; I have lately however seen some very good bells^
made by Messrs. Taylor of Loughborough ; and I have had
the opportonity of comparing one of their beUs with a
foreign one imported by Mr. Dent for trial, and the Eng«
lish one was decidedly the best. And therefore, though
the casting of bell-metal is a 'mystery^ requiring consider-
able skill and management beyond merely melting together
certain quantities of copper and tin> there is no reason
to reckon bell-founding yet among the artes perditce* If
people would always reject bad bells, good ones would soon
become as common as they ever were.

TIME OF STEIKING FIEST BLOW-

171. It is usual to make the quarters let off the hour ;
that is, the locking-plate of the quarters is furnished with
a pin or a snail which, while the last quarter is striking,
performs the office of the discharging pin on the hour wheel
•of the going part when there are no quarters. And for
ordinary clocks this plan does well enough ; but it is evi*
dent that in that case you cannot rely on the first blow of
the hour, which is the proper indication of the exact time,
being right to several seconds, because it depends on the
rapidity with which the quarters may happen to strike, in
addition to the ordinary sources of inaccuracy in the time
which 4he &our train takes to get into action; both of which

TEAIN EEMONTOIBES. 231

differ considearably in different states of the clock. And
therefore in some clocks there are two snails set on the
honr'^wheel^ one of which lets off the quarters^ from a quar-
ter to half a minute before the hour^ and the other snail
lets off the hour striking part exactly at the hour. And
here I may remark^ that the larger the snail is the more
accurately it will let off^ because the linear space on its
circumference. corresponding to one beat of the clock will
be larger^ but the more friction it will cause. Moreover^
if the time of striking the first blow is intended to be very
accurate^ the hammer should be left on the liffc^ or just on
the point of fallings instead of having to wait while the
train is raising it. And in that case (and indeed it is better
to do so whether the hammer is left on the lift or not)
there should be a small click applied to one of the wheels
of the striking train to prevent it goiag backwards when
the clock is being wound up. Mr. Dent uses merely a
single pin^ set as a tooth into the fi^y arbor^ and so placed
that the click falls against it when the clock has done
striking*

TRAIN EEMONTOIEES-

172. This naturally leads to the subject of remontoireB
in the train, which I have several times referred to> and
which are quite distinct from remontoire escapements. If
the scape-wheel^ instead of being driven directly by the
train and the clock weighty is driven by a small weight
which is wound up at every twenty or thirty seconds by the
clock train, the clock will have these advantages : lat. The

m TURRET CLOCKS.

scape- wheel will be driyen by a force as nearly uniform as
possible^ being free from all the inequalities of the friction
of the train and dial work^ and the effect of the wind upon
the hands. 2ndly, The striking may be let off more ex-
actly than in the common way^ because the snail will turn
through a fifteen times larger angle if let off by the re-
montoire every thirty seconds than by the pendulum every
two seconds ; and so you may be quite sure that the striking
will be let off at the sixtieth second of the sixtieth minute
of the hour, which you cannot secure in the common way.
Srdly, The long hand will move a visible distance by jumps
at every half minute, which will enable a spectator to ob-
serve the time as accurately as from the second-hand of a
regulator ; whereas in common turret clocks the time can
hardly be taken to less than a half a minute even in the
most favorable positions of the minute-hand. In short by
the use of a remontoire in the train a dock would go
better, and would also be available as a regulator both by
sound and by sight, as perfectly as an astronomical clock ;
while a common turret clock, if it goes ever so well, is
useless for very exact observations, such as a person wanting
to regulate a good clock of his own would require, as he
can neith^ tell the time from the hands nor rely on the
striking to several seconds.

178. There have been various contrivances fortius pur-
pose. One is described by £eid as having been put up by
him at Edinburgh in the last century, which was worked
by a Huygens's endless chain (79). He says it went very
well, but that the chain and other parts connected with it
wore out so fast that it was removed. There have been

EXCHANGE CLOCK REBCOKTOIRE. 233

many attempts at it in France^ but they are stated in Erench
books on the subject to have been irenerally unsuccessful.
However a public clock with a remontoire i the train ha.
now been going for five or six years in London; and the
efficacy of it as regards time keeping may be judged of by
any of the numerous chronometer-makers who live within
sound of the Exchange bells; and any person may judge
of the effect of it as regards the other objects I have men-
tioned by looking at the long hand just before it strikes the
hour : he will see the last jump of the hand, after the quar-
ters have done striking, take place at the same moment as
he hears the first blow of the hour. And as the great
clock for the new palace at Westminster is to have some
contrivance of this kind, a description of it will probably
be interesting.

Any person with a moderate amount .of ingenuity will
.see.that the only real difficulty iji]the problemis to keep. the
action of the remptitoire weight on the scape-wheel while it
is being lifted. Harrison's going ratchett might of course
be applied; and although it would cause a small amount of
friction, it would have some advantages perhaps over the
one I am going to describe. The plan of the Exchange
dock remontoire is this, omitting some merely mechanical
details. The wheel D, whose pinion is driven by the centre
wheel £, has int^iud teeth; and a wheel €, which rides
upon the arbor of D, has external teeth as usual. On the
arbor of D there rides also ah arm or lever G B A, carrying
the remontoire weight A; and there is (or may be con-
sidered to be) a pin or stud upon the arm for a wheel B to
lide upon, which works between the ext^nal teeth of G and

TTJfiBET CLOCKB.

t^e uLternal teeUi of D. Consequently, whenerer the wheel
D ia driven by the train it will raise GiB right aie of B,
which will raise the lerer and the weight; bat t^e left side
of B will nererthdeas be always pressing downwards on C
and tending to tnm it the opposite way to D ; and therefore
a large wheel F fixed to the whed C may be employed to
drive the scape-wheel^ which will then be driven merely 1^
the remontoite weight and not by the clock train.

174. The mode of letting off the train at every twenty
seconds is this. The scape-wheel arbor tnms in a minute
and is nearly half cut throogh in three places near together;
and on the rim of B, which is made broad enough for the
purpose, are placed three sets of spikes in diffa^nt planes
corresponding to the three nicks in the scape-wheel arbor;
and these three nicks being made at uiglea of 60° to eadi

EXCHANGE CLOCK REMONTOIRE. 235

other, they come successively at intervals of twenty seconds
into such a position that a spike of one set can pass through
the corresponding nick, hut a spike of the next set strikes
the arhor in a place where it cannot get through for
twenty seconds more, and then a spike in the third plane i$
stopped in the same way, and so on. Thus at every twenty
seconds the wheel D is allowed to move through the space
between two spikes, and so the Uttle weight A is raised
through a small space by the force of the clock train, and
the forcQ on the scape-wheel is the same upon the whole
for every successive third part of a minute, though during
the twenty seconds it varies a Uttle as the distance of A
firom a vertical line through C varies, by reason of its des-
cribing a circular arc.

Half a minute would be a better interval than twenty
seconds, because it is not easy to see at a distance whether
the hand is ten seconds before or after the half minute^
and the motion at each move would also be half as much
i^aiii for thirty seconds as for twenly.

175. The plan which is adopted in the French turret
docks, which I understand are now generally made with a
remontoire in the train, is the same in principle, only in-
stead of a wheel running between the internal teeth of one
wheel and the external teeth of another, a bevelled wheel
riding on the remontoire arm runs between two other
wheels at right angles to it, as shown in the next drawing.
The wheel D performs the o^ce of the internal wheel D in
the Exchange clock, raising the weight A by means of
the wheel B, which turns freely on the remontoire arm,
and so always presses dQwnwards on C, to which is fixed^

236

tubrbt clocks.

as before, ihe
wheel P irhich
is to drive the
scape - vheel ;
and the broad
wheel, with the
three rows of
spikes in it, is
fixed to D, as
before. I do
not know that
eith^ of these
methods is bet-
ter than the other, except that, as it is impossible to cat
bevelled teeth to the right shape as traly as flat ones, there
is probably rather less Motion in the internal wheel plan
than in the other ; but it is also the more expensive of the
two.

But there is this objection to both of than, that the
■pikes strike the acape-wheel arbor with considerable force,
and even while they are at rest press upon it pretty heavily,
and therefore a larger force is required to drive the scape-
wheel. The force of the blow has been somewhat dimi-
nished in the Exchai^ clock by putting a spring with a
concave face for the spikes to slide up before they reach
the ubor. In tiie more recent French clocks, it is done
by making the train drive a fly, which moderates its velo-
city ; tuid iu some of them the spikes are pnt on the end
of the fly, or an arm on the fly arbor, which is a very great
improvement, as it also diminishes the constant pressure

FRENCH TRAIN REMONTOIRE. 237

and friction on the arbor of the scape-wheel^ in the ratio of
the velocity of the spikes when set on the second wheel to
their velocity when set on the fly. They have also been
■^. .0 ... Iff by . Wer lie . .^g pL, inete^i o, b,
nicks in the arbor; but that method gives the scape-wheel
more to do^ and produces much greater friction. This
IjLOwever would not signify where there is a remontoire
escapement as well as a remontoire in the train ; and per-
lliaps for a very large clock with such an escapement this
might be found the best way of letting off the train remon-
toire^ since in that case the pressure or blow of the spikes
is immaterial^ as it does not fall on the scape-wheel arbor.

CONTINUOUS MOTION REMONTOIRE.

176. A very ingenious and curious application of the
gravity remontoire has lately been made by a French clock-
maker^ named Wagner^ for the purpose of obtaining a con-
tinuous motion of the heavy part of the train combined with
the accuracy of a vibrating pendulum driven by a constant
force. Instead of the remontoire being let off at definite
intervals by the scape-wheel, the bevelled wheel D works a
fly, by the intervention of two or three intermediate wheels.
This fly revolves horizontally below the clock frame, for a
reason to be explained presently. If the fly always turned
at a constant and proper rate, it would evidently let the
driving wheel D turn one way just as much as the opposite
wheel C turns the other way, under the action of the escape-
ment and the remontoire weight, in any given number of
seconds; or, in other words, those two wheels between

838 TUEROT CLOCKS.

them would always keep the remontoire arm at the same
height. Now this arm is prolonged to a convenient length,
and from its end is hung^ by two wires, a thing like a gonff,
suspended horizontally, and with a hole in the middle for
the fly arbor to pass through; and this gong, or bell, is so
placed, that when the remontoire is at its medium height
the beU. about half covers the fly, which tarns within it :
if the remontoire falls below its medium height the bell
will evidently fall, and more completely enclose the fly ;
and the effect of this is that the air within the beU becomes
rarer by the action of the fly, and consequently offers less
resistance to the fly, which will therefore regain its proper
velocity ; and of course an increased velocity of the fly is
identical with an increased velocity of the traiu, which was
previously going too slowly to keep up with the regular
motion of the scape-wheel. And in like manner, if the
train and fly are going too quickly, the bell is lifted up,
and the fly more exposed to the external air, which offers
an increased resistance, and so again restrains the velocity.
There is indeed, theoretically, a much more simple way
of combining a continuous motion of the train with a
vibra-ting pendulum. Por if any point in a heavy pendulum
is connected by a long horizontal rod with a crank, or a pin
set on the face of a wheel, moving in the same plane as the
pendulum, and the pendulum is made to swing just so fiEir
as to let the crank turn round iu one double oscillation, it
may be easily proved that the natural velocity of the given,
poiut in the pendulum is the same in every position as the
velocity, iu a horizontal direction, of the end of the crank,
the crank itself revolving uniformly. The practical diffi-

TRAIN REMONTOIRES. 2S9

cnlty^ however^ is to keep the pendulum always vibrating
the same arc^ when there is a variable force acting on the
crank, without which it would not answer.

SPEING KEMONTOIKB.

177. Instead of a weight acting on one of the wheels of
the train, as in any of the preceding methods, a spring may
be used to communicate the force from the pinion of the
scape-wheel, or the wheel below it, to the wheel itself.
And a spring possesses these great advantages over a^
weight, that it requires no maintaining power to keep it in
action when winding up, as I explained in the case of a
spring clock without a fusee (80), and that it acts without
any friction. These advantages are so great, that I have
no doubt a spring remontoire may be made better, and
a ^, ^j J^ eh»p», 1. », g.^ ^

There is a description of a spiral spring remontoire let
off by nicks and spikes, as before described, in the Ency*
clopsedia Britannica. And I have lately seen some small
Prench clocks with a spring remontoire on the second
wheel, and I am told at Mr. Denf s they go better than
ordinary French clocks without a fusee, which, however, is
not saying much for them. The spring should, if possible,
be put on the arbor of the scape- wheel instead of the
second wheel, because then it acts without any friction
of the scape-wheel pinion ; in fact, the scape-wheel then
has no pinion, properly speaking.

But all the remontoires of this kind that I have seen or
read descriptions of, are liable to the objection that either
the wheel or its pinion rides upon the arbor of the other of

24ft TDREET CLOCKS.

them, as in Mr. Air/s eacapement (47), which caxiBes the
wheel to turn with considerable friction ; and from this and
other causes, the spring remontoiies that have been hitherto
made, especiaUy in turret clocks, do not appear to have
given satisfaetion. I shall therefore describe one which has
been lately made, and in which the objection I have just
now mentioned is removed, and some other advantages
obtained, and which is perfectly easy to constmct, aoid at a
moderate expense.

The lai^ wheel in this drawing, which is the second or
centre wheel (there being only three in the train} drives a
pinion of 14 leaves, which ridea on a stud or fixed arbor
screwed into the clock frame; and the pinion is also pro-
longed into a pipe large enough to enclose, without toneh-
ing, the brass bush, which is fixed on the end of the stud
to form a pivot-hole for the scape-wheel arbor. On this
pipe is fixed a spiral spring, (the mainspring of a moderate-
sized musical box), of which the outer end takes hold of a

SPRING REMONTOIEE, MEANWOOD CLOCK. 241

pin set on the back of the scape-wheel. It is evident there-
fore, that if the pinion and pipe are turned round or wound
up from time to time, it will wind up the spring, and the
sca^e-wheel wiU be driven by the spring without any fric-
tion at all, except that of its own pivots ; and also that
whenever the second wheel is let go, it will so turn the
pinion and wind up the spring.

The letting oiBF is not done in the same way as in the
Exchange clock, but the wheel drives another pinion
(marked 7) on an arbor which carries a fly; and this fly,
(though not so exhibited in the drawing) may have at its
ends the spikes which axe to slip through the notches in
the scape-wheel arbor as before described. Now, as-
suming the scape- wheel to turn in two minutes (which is
more convenient than one miuute for turret clocks) and the
lemontoire to be let off every half minute, the letting off
would be done by a four-armed fly set on a pinion of the
same number as the scape-wheel pinion, and four notches in
the scape- wheel arbor acting as the three do in the Exchange
clock. But I have also made an alteration in this respect,
for the purpose of diminishing still further the pressure of
the spikes on the scape- wheel arbor, and getting a larger
motion of the fly in proportion to the same motion of the
train, and consequently a slower motion of the train during
its action. The scape-wheel arbor comes through the frame
and ends in a cylinder, of which the face has two nicks cut
across it, one broad and i inch deep, and the other narrow
and i inch deep; and therefore if one end of the fly
has a short and broad pin properly placed, it can slip
through the broad nick only ; and a long and thin pin

242 TURRET CLOCKS.

at the other end of the fly will slip through the narrow
nick only, when the nicks respectively come into a posi-
tion at right angles to the fly. In this way the two-
armed fly is allowed to tnm half round at every quarter
of a revolution of the scape-wheel ; and as the fly pinion
has seven pins while the other has fourteen, the remon-
toire spring is wound a quarter round at every l^t off of
the remontoire. The second wheel, which drives them
both, turns in eighteen minutes, and consequently if the
spikes were set on it instead of on the fly, their pres-
sure on the scape-wheel arbor would be 36 times as great.
I found this pressure amount to barely two ounces, with
a very heavy weight on the clock ; and as it is made to act
upwards, it only relieves the pressure of the arbor and the
cylinder on the adjacent pivot-hole.

The spikes or pins are not really set on the end of the
fly, but on bent springs about three inches long, in order
to diminish the force of the blow on the scape-wheel arbor,
and the too sudden stoppage of the train ; and for the pur-
pose of doing the same thing more completely, and also
stopping the recoil of the fly after the blow, there is a fric-
tion spring set on the frame, which the fly has to slide over
just before it reaches the cylinder; this of course diminishes
its velocity or momentum when it is greatest, and also acts
as a click which the fly cannot pass in recoihng.

It remains to be explained how the adjustment of the
remontoire spring is made, in case it is found to give too
much or too little force to the scape-wheel. The fly is not
fixed to its arbor, but it has a click that takes hold of a
ratchett with ten or twelve teeth, fixed to the arbor in the

SPRINO REMONTOIRE, MEANWOOD CLOCK. 243

usual manner of the striking fly ratchett. Therefore when
you want to alter the tension of the spring you have only
to lift the click, without stopping the clock, and shift the
ratchett as many divisions as may be necessary, which will
turn the scape-wheel pinion and spring just half as much
as you turn the fly arbor, since the scape-wheel pinion has
twice as many pins as the fly pinion. The ratchett is made
with square teeth, which are also numbered, for greater
safety of action and certainty in adjusting it. The spring
must of course be occasionally cleaned and oiled, to keep
it from rusting, and so should the pendulum spring.

This is the construction of the clock represented in the
;-&'ontispiece, which is just completed for the newly built
church at Meanwood, near Leeds. It is of course too soon
as yet to give any account of its performance as regards
time-keeping, but its mechanical action is quite satisfactory ;
and as that is the only novelty in it, the principle of the
spring remontoire having been tried for some time, I see
no reason to doubt that it will be altogether successfuL
The going weight required is about half as much again
as it would be if there were no remontoire, because all train
remontoires require additional weight to overcome the ad-
ditional friction, and to wind up the remontoire with-
out any hesitation; but as none of this additional force
reaches the escapement it is of no consequence, and you
can put on weight enough to drive the hands in all weathers
without at all affecting the swing of the pendulum; whereas
in a clock without a remontoire you cannot put on weight
enough to drive the hands in bad weather and when the oil

is frozen, without making the pendulum swing too far as

244 TURRET CLOCKS.

soon as it becomes wanner. I have seen the semi-arc of
the pendulum of a church clock, and a very good one, vary
nearly a degree between winter and summer.

Another effect of this remontoire is the remarkable silence
of the beat, as compared with the Tavistock clock in which
the wheels are of the same size, or with the Exchange clock
in which the momentum of several wheels and the re-
montoire weight has to be stopped by the pallets at every
beat ; whereas in this clock the only thing to be stopped is
the scape-wheel, which is less than four inches in diameter
and only moves 4^° at each beat. It is probable also that
it follows the pallets more closely when moved by a spring
than when, moved by gravity. This silence of course in-
dicates that there is less waste of force at each beat in a
clock with a spring remontoire of this kind than either
without any remontoire or with a gravity remontoire.

178. I have hitherto spoken of the ^(?fo^t<?a^ advantages
of a train remontoire. But it has besides the economical
advantage of superseding the necessity for highly finished
wheels in the lower part of the train, as it reduces that
part merely to a machine for driving the weight of the
hands and winding up the remontoire, instead of being a
machine for transmitting to the pendulum as uniform a
force as possible. And therefore I see no reason why the
great wheel, hour-wheel, and all the leading-off or bevelled
wheels (of which sometimes as many as nine are necessary)
should not be of cast iron instead of brass, which it seems
would almost cause their cost to be measured by shillings
instead of pounds. If it had been certain beforehand
that this new remontoire would answer, the Meanwood

CAST IRON WHEELS. 245

clock would have been so made. I know that there is a
prejudice against cast iron clock wheels even in the striking
part. But people would easily see that this prejudice is
unfounded if they would only remember that the striking
part of a clock is nothing but a machine for raising a heavy
hammer 156 times in a day, or rather in ten minutes, since
it would strike 156 in about that time if allowed to go on ;
that all you want is sufficient force to do this without any
unnecessary wear of materials ; that (as I have shown) cast
iron clocks are now doing this work with considerably, fe**
waste of power and therefore less wear of materials than
the best brass clock probably in the world ; and lastly that
such clocks can be made much cheaper than brass ones
equally good. And when the going part is also reduced,
as it is by a remontoire, to a mere weight-raising machine
in which uniformity of force is of no consequence, there
will be no more necessity for brass wheels there than in the
striking part. The only question was whether a remon-
toire could itseK be made at a moderate expense ; and it
now appears that it can ; indeed I was led to turn my at-
tention to the contrivance of such a remontoire by a
remark of Mr. Denfs, that a good and cheap remontoire
was essential to any further material improvement in turret
clocks, especially large ones ; and it may be added that a
good (that is, a secure) and cheap maintaining power or
' going barrer apparatus was equally essential to the making
of such large clocks except at an enormous increase of their
cost, and I think that difficulty has also been removed as
described in § 159.

179. I have spoken throughout of bra^s wheels;

246 TURRET CLOCKS.

meaning thereby either brass or gun-metal, which is a com-
pound of copper and tin instead of copper and zinc^ with
a lower proportion of tin than in bell-metal. The pro-
portions for the best gun-metal are^ I understand^ &om
92 copper -I- 8 tin to 90 copper -f- 10 tin; and such metal is
harder than the best hammered brass^ and yet not too
brittle for the teeth of wheels. It is however a difficult
metal both to make and to work : the castings^ especially
large ones^ being often full of defects, consisting not only
of holes, but of hard pieces which are as destructive to
wheel-cutters as a cinder in a piece of bread is to human
teeth ; and it is in any state a very tough metal and clogs
the files. I am informed however by the best authority on
this subject, that these defects in the casting may be pre-
vented by not putting the tin to the copper at once in the
above j^oportions, but previously making an alloy of 2
copper + 1 tin, which they call 'hard metal,' and which is
the ' highest' compound the metals admit of without the
excess of tin beginning to make the alloy softer again : to
this alloy the further proportions of copper are afterwards
added; and in order to obtain the greatest density or
specific gravity which the compound admits of, the castings
are always made with a long ' dead-head' to produce con-
siderable pressure on the fluid metal. I am told also that
adding a very small quantity of zinc, about 1 per cent.,
makes the metal both more fluid in the crucible and more
compact when cold. The Specific gravity of metal cast in
this way at Woolwich has been known to be as high as
9, and is generally about 8*75, while that of brass is only
8*37 (according to the ' data' in Weale's Dictionary).

GUN-METAL. 247

180. I think it is also worth the consideration of clock-
makers whether they could not get more true and sound
cast^igs^ either of brass or gun-metal^ and such as would
suffer less waste and require less labour in squaring out and
turning up, by having cast-iron moulds made for the sizes
of wheels they are in the habit of using. Large castings,
even in brass, are often defective for as much as ■^^th of an
inch deep ; and I understand a very sharp and clear cast-
ing can be obtained from a heated iron mould instead of a
damp sand one, since it does not chiU the metal too soon
but lets it run into the smallest comers. The part of the
mould between the spokes would have to be made separate
and bevelled a little, so as to lift up, and let the wheel
contract in cooling, or it would probably break itself; and
the mould should not be an open one, but close, and with
a longish pipe to it, by way of a ' dead head,' to produce
pressure upon the metal, as the effective part of bells, viz.,
the mouth, lies at the bottom of the mould. These how-
ever are only suggestions, which some person better versed
in the art of brassfounding may perhaps reduce into a more
practical shape. The necessity of some improvement in
this art will be evident when I state that three brass cast-
ings were made for the great striking wheel of the Tavistock
dock before one was obtained sound enough even to cut
for the model ; and more, I believe, for the great wheels of
the Exchange clock, which are of gun-metal, as those of
the Parliamentary clock are required to be, in my opiaion
very unnecessarily as regards all but the escapement part of
it, in such a large clock : I mean of course that they should
be of iron. This diflBculty of getting really good gun-metal

24.8 TUBJ(,BT CLOCKS.

castings^ hard enoagh to be any better than brass^ causes
some, clockmakers to prefer, well-^hammered brass to such
gun-metal as they can be sure of obtaining from the foun-
ders. At any rate however the bushes, which are too
.thick to.be hardened throughout by hammering, and in
wliich brittleness. does not signify, ought to be made of
guurmetal; but it should be free from hard bits, whidi
would probably cut the arbors. It must not be forgotten,
moreover, that gun-metal is more expensive than brass, both
in the making and the working.

181. Lastly, all the iron work> whether cast or wrought,
and whether visible or invisible, except just the acting sur-
faces, ought to be painted. Polishing it does no good, cbstis
money, and requires continual cleaning and oilmg to keep
it from rusting. This rule has been followed throughput
in the Meanwood clock, though it is one in which, as the
reader has seen, no expense was spared that was thought
likely to produce any useful effect.

And with regard to this rather important matter rf
oiling, fresh oil ought never to be put on, especially on the
escapement, without thoroughly wiping the old oil off. I
have had to take out a scape-wheel and wash it with soda to
get off the accumulations of oil with which an attentive
sexton had lubricated it in the course of two or three years.
The pivots should have clean oil whenever they appear to
be dry; but. the pinions should only be wiped with an oily
cloth, and not have: oil dropped on to them, as is the com-
mon practice; and this applies to house.clocks as well as
church clocks. Asfaras my experience goes; I think no
oil equal upon the whole to some which was recommended

OIL. 249

to me at Mr. Dent's for the purpose of preserving steel
surfaces from rusting: it is neafs foot oil, well-stirred
about in water, skimmed off and filtered once or more
through blotting paper until it is quite clear. Though it
is the most filthy looking stuff at first, it produces at last
an oil more fluid than the best sweet oil, and which has
the important advantage of never freezing, nor forming a
brown cake on iron, as the vegetable oils do; I should
think, therefore, it is peculiarly suitable for church clocks :
indeed I have applied it to a house regulator for some
time, and, as far as I can judge, with very good effect.

18ii. The pulleys for church clocks require more atten-
tion than they frequently receive, especially as the fixed
pulleys are often put high up in the tower, where the
oiling of them, is neglected. Every pulley ought to be as
large in diameter as it conveniently can be made, for the
obvious reason, that the larger it is the slower it has to
turn. I should say that no pulley for a moderate sized
clock ought to be less than nine inches diameter, nor less
than twelve inches for a large clock with heavy weights.
Another point, which is of perhaps even more importance,
is, that the pivots, or arbor, should be fixed into the
pulley, and not a pin put through a hole in the pulley, as
the common pulleys for raising weights are made, in which,
for various reasons that I need not specify, it is of less
consequence than in clocks. For when the pin goes
through a hole in the pulley, it requires to be much thicker
than pivots turning in bushes set in the frame, in order to
obtain the same strength; and therefore the friction is

greater, and the weight required to drive the clock greater,

25a PULLETS.

and the wear of the pin and the hole in the pulley greater
than it need be. Secondly, the effects of this wearing are
much more mischievous ; for pivots always pressing in one
direction only wear a hole larger in one direction, or make
it longer, and it will therefore work in it with no more
friction at last than at first; whereas when the hole in a
riding pulley is worn bigger, the friction is increased as
much as if the pin had been originally made so much
larger; and indeed more, because the bearing surface of
the pin is narrower than if it were as large as the hole.
Lastly, a fixed arbor, with brass bushes screwed into the
pulley frame, keeps the pulley much steadier, and with
more equal bearing on both sides, than a pin. Pnlleys
made as I have described of course cost rather more than
those made in the common way, but they are very well
worth the additional expense.

183. There are two or three other matters which should
be attended to in putting up church clocks. One is to
enclose them in a wooden box that locks up, leaving the
winding squares open, so that the clock can be wound with-
out unlocking the case, and so that nobody but the person
who has the care of the clock can get at the works. The
pendulum should also be enclosed all the way up. And it
is essential to the keeping of a clock in good order that
the place where it stands should be light : if it is not
light already, it should have a window put in before the
clock is put up ; and if the architecture will not allow it
anywhere else, the middle of the dial may be, and often is
with good effect, made a window. When the clock is a
good one, worth looking at, it is a good plan to have some

BOX FOR CLOCK. 251

smiall panes of plate glass put in the doors of the box or
case, so as to show the escapement and the regnlating dial,
which, if the clock stands in the belfry, will serve also for
a dial for the ringers. If the bottom of the pendulum
comes in a convenient place, it is as well to put a piece of
glass to show the degree plate, so that anybody can see
how far the pendulum is swinging. All these little things
tend to make people careful of their clock when they have
got a good one. Mr. VuUiamy mentions several public
clocks in Paris which are fitted up with glass, so that they
can be completely seen without opening them; and the
same thing has lately been done at the Exchange clock,
and is contemplated by the astronomer royal for the Par-
liamentary clock.

184. Not long ago, I heard that the weight of a church
clock in London had broken the rope and fallen (as a
weight of several cwt. easily would do) through the belfry
floor and the pavement of the church into the vaults below.
This accident, which is not very unconmion, is most likely
to arise from the sudden stoppage of the weight when it is
wound up until the sexton feels he can wind no farther ;
and with the view of stopping him in time, a string may be
put to each weight and over a small pulley at the top, and
the other end, with a little weight attached to it, made
to come down close by the place where the clock is wound
up ; so that when the great weight is up, the little weight is
down, and the man will know that it is time to stop wind-
ing. This is like the weight put to an organ to show the
blower when the bellows are fall. Where the weights come
down on to a floor over the heads of people in the church,

252 GREAT WESTMINSTER CLOCK.

it is prudent to put a large box filled with wool or sawdust
on the floor, where they would fall; the wool or sawdust
need not be left open, but should be covered up with
boards, which will only break first if a weight falls.

THE GBEAT CLOCK FOE THE NEW PALACE

AT WESTMINSTEE.

185. I have no doubt that it will be interesting both to
clockmakers and to other persons to know what has taken
place up to this time with regard to what may be called
the National Clock, both on account of the building on
which it is to be placed, and because it is intended to be
the best and largest public clock in England, and in the
world.

Six years ago, viz. in March, 1844, Mr. Barry, the
architect of the new Houses of Parliament, wrote* to Mr.
Vulliamy, to ask if he would furnish him with a plan for the
clock; and as he could not undertake that Mr. Vulhamy
should be employed to make it, he inquired upon what
terms he would furnish the plans, first, in the event of his
being employed to make the clock, and secondly, of his not
being employed. Mr. Vulliamy, in reply, proposed that, if
employed, he should be paid 100 guineas for the specifica-
tion, calculations, working and other drawings ; and if not
employed, an additional 100 guineas for his time and
trouble.

* I may as well state that I shall follow the words of the corre-
spondence as nearly as I can conveniently, and without perplexing
the reader, printer, and myself, by contyiual quotation marks, and
interruptions of them.

CORRESPONDENCE. 253

' Shortly af(:erwards Mr. Barry wrote to the Board of
Woods and Forests, saying that, owing to the progress
making with the clock-tower, it was desirable to have the
necessary specifications, working drawings, and estimates
prepared ; and that he had therefore applied to Mr. Vulliamy
as, in his opinion, the person best qualified to make out such
specification, working drawings, and estimates ; and he for-
warded the two preceding letters, and recommended that
Mr. Vulliam/s offer be accepted. In a few days he re-
ceived an answer from the Board conveying to him the
requisite authority to engage Mr. Vulliamy upon the service,
and upon the terms named in Mr. Barry* s letter. This was
of course communicated to Mr. V., who replied that he
should proceed without delay to prepare the plan of the
clock for Mr. Barr/s inspection.

In January, 1845, however, Mr. Vulliamy wrote to
Mr. Barry, to say that he had just observed a mistake
\ in the letter from the Office of Woods and Forests, viz.,
^ that though Mr. Y. had said nothing about an estimate,
\ the Board had incidentally introduced the word, no doubt
I as a matter of course ; and that to make an estiniate would,
^ until it is definitely settled how the clock is to be made, be
quite useless; and would be a work of great labour, occu-
pying much time, and not contemplated either by himself
or Mr. Barry ; and that he thought it right without delay
to notice the circumstance, lest it should give rise to any
misunderstanding afterwards.

To this letter there appears to have been no answer from

Mr. Barry, or notice of it by the Board, except so far as the

\ subsequent letter of Mr. Barry, of July, 1846, is an answer.

264 GREAT WESTMINSTER CLOCK.

In November, 1845, Mr. Dent wrote to the Board, to
say that he was desirous of being admitted as a candidate
for supplying the large clock, and such others as might be
required for the new Houses of Parliament ; and by way of
recommendation he referred among other things to the tes-
timonials of the astronomer royal and ,Mr. G. Bennie, re-
specting the Exchange clock, and proposed to obtain the
sanction of the Board for erecting the new clock, subject to
the approbation of the astronomer royal, with Mr. Barry,
and Sir John or Mr. George Eennie, as referees. The
Commissioners answered that when the drawings and sped-
fications for constructing the great clock were completed
and could be submitted to the several clockmakers who
might be applied to, as the basis upon which their tenders
were to be founded, the Board would include him as one of
the competitors, for making that as well as any other clocks
that may be subndtted to competition.

To this Mr. Dent replied, that if adherence to draw-
ings and specifications to be prepared by another clockmaker
were to be stringent on him, he must decline to become a
candidate; that he should feel it a duty to comply with any
suggestions from the astronomer royal, but could not
engage to act under the directions of authority less emi-
nent, or to follow instructions, which by degrading him to
the position of a mere executive mechanic, would prove de-
trimental to his reputation.

Apparently in consequence of this letter, though after
an interval of some months. Lord Canning wrote to Mr.
Airy, to ask his opinion, as it was of importance that the
clock should be the very best that the science and skill of the

COKRESPONDENCB. 255

eouniry can su^ly, whether the best means of obtaining
such a clock would be to call upon some of the most emi-
nent clockmakers to send in specifications^ drawings^ and
estimates, of the clock which each would recommend and
would be prepared to make ; or whether it would be better
to place the matter in the hands of some one experienced
mechanician, and to adopt the description of clod which
he might recommend, leaving the execution of it open to
tender ; and he requested the astronomer royal to send him
the names of the persons or person he would recommend
for the service in either case.

Mr. Airy repKed that a nearly sinular question was ad-
dressed to him in 1843 by the Graham Committee with
respect to the Exchange clock, and that he then replied
that certain conditions ought to be laid down, which he
would furnish, and that the clockmakers^ plans should also
be submitted to him for his opinion, and that the Commit-
tee should refer to him for a certificate at the completion of
the work: that those conditions were adopted by that
Committee; and that the result is that a clock has been
put up, which is superior even to most astronomical clocks,
and possesses these rare advantages, that the first stroke of
each hour is correct as to time within less than one second,
and that a person standing on the pavement can take time
from the face without an error of a second. Mr. Airy
therefore proposed that a similar course should be followed
here. He says that he suggested to the Gresham Commit-
tee the names of Mr. Vulliamy and Mr. Whitehurst; but,
by arrangements with which he was not acquainted, the work
was placed in the hands of Mr. Dent, chronometer-maker

256 GREAT WESTMINSTER CLOCK.

(f . e, before that time not a tuiret-clock maker) ; and he
was bonnd to- say that Mr. Dent had carried out his views
most completely^ making in the mechanical arrangements
which he (Mr. Airy) had suggested some judicious altera-
tions^ which received his entire approval. Under all the
circumstances^ considering that a new clock pretending to a
degree of accuracy equal or superior to that of the Ex-
change^ must probably contain some of Mr. Dent^s inven-
tions^ and would at any rate be improved by his experience,
that the trust is^ so to speak^ confidential, and that there
is no such thing as a market for such clocks — ^Mr. Airy
thought it would probably be the best course to transmit
proposals (including his enclosed conditions) to Mr. Dent,
and to ask for his tender; and if his price should not
be excessive, that he should be employed : if it appeared
objectionable, other makers should be apphed to ; but he
thought only the two he had named.

The Board did not however adopt Mr. Air/s recom-
mendation to apply in the first instance to Mr. Dent ; but
Mr. Barry a few days afterwards, iti July, 1846,* wrote to
Mi*. Vulliamy to inform him that the Board had deter-
mined to invite the tender of plans and specifications from
.different quarters for the clock ; to be based upon the en-
closed general conditions prescribed by the astronomer
royal, who (Mr. Barfy stated) had recommended that ap-
pHcation should be made to Mr.; Dent and Mr. Whitehurst
as well' as to Mr. VuUiamy. He also informed Mr. V.
that if he should have acquired any information which

* It may be observed that just at this time Lord Canning re-
signed, and was succeeded by the present Lord Carlisle.

MR. airt's conditions. 257

might lead him to suggest a departure from the enclosed
conditions he was at liberty to do so in sending in his
plans. And further that the Board considered it conve-
nient that he should submit the estimated cost of supplying
and completing the clock in all respects according to the
conditions.

186. The following are Mr. Air/s 'Conditions to be
observed in regard to the construction of the clock.
; '1. The clock frame is to be cast-iron, and of ample
strength. Its parts are to be firmly bolted together ; where
.there are broad bearing surfaces, these surfaces are to be
:planed.

' 2. The wheels are to be of hard bell- [gun-] metal, with
.steel* spindles working in bell-metal bearings, and proper
holes for oiling the bearings.* The teeth of the wheels are
to be cut to form on the epicycloidal principle : [nothing is
jsaid about the pinions, of what shape or material they are
.to be.]

/3. The wheels are to be so arranged that any one can
be taken out without disturbing the others.

/ 4. The pallets are to be jewelled.

'5. The escapement is to be dead-beat, or something
equally accurate, the recoil escapement being expressly
excluded. '

' 6. The pendulum is to be compensated.

* This is a mistake : such holes are unnecessary and mischievous,
as they will let in dust, which will do more harm to the pivots than
want of oil would, and clock pivots can be oiled perfectly well without
lioles. In heavy machinery going with considerable speed, and re-
quiring a great deal of oil, the case is different.

258 GREAT WESTMINSTER CLOCK.

' 7. The train is to have a remontoire action^ so con-
structed as not to interfere with the dead beat principle of
the escapement.

' 8. The clock is to have a going fusee [barrel. No
particular kind of going barrel is here specified, but it
appears from the subsequent papers that one similar to
that in the Exchange clock is intended.]

^ 9. It will be considered an advantage if the external
minute-hand has a discenuble motion at certain definite
intervals of time.

^ 10. A spring apparatus is to be attached, for accele-
rating the pendulum at pleasure during a few vibrations:
[this wiU be explained presently.]

'11. The striking machinery is to be so arranged that
the first blow for each hour shall be accurate to a second
of time.

' 12, and 13, [relate only to a possible electrical con-
nexion with the Greenwich Observatory for the purpose of
making the clock report its own behaviour to the astrono-
mer royal.]

' 14. The plans before commencing the work, and the
work when completed, are to be subjected to the approval
of the astronomer royal.

'15. In regard to articles 5 to 11, the maker is re-
commended to study the Exchange clock.'

188. An explanation will probably be required of the
apparatus referred to in the tenth of these conditions. It
is evident that a clock with a two seconds pendulum cannot
be altered by any less amount than two seconds, without
handling the pendulum in a manner which is both difficult

PENDULUM ACCELERATOR. 259

and unsafe with a heavy pendulum. Mr. Airy therefore
contrived for the Exchange clock an apparatus which
enables it to be set to any fraction of a second. It con*
sists of a long spring set upright upon a frame which slides
under the pendulum bob, and is so arranged that by
pulling a string in the clock room the frame can be brought
into such a position that the spring hits the pendulum at
every swing in one direction, which accelerates its vibration
a little. Therefore, if the clock is a few seconds too slow,
the man merely puUs up the string, and holds it till he
observes the second-hand and the beat of the clock agree
exactly with that of the chronometer in his hand. If it is
a few seconds (not an even number) too fast, it is first put
back one beat too much, and then accelerated to make it right.
I may observe here, that a clock should never be altered
by taking hold of the pendulum anywhere but at the bob ;
and indeed it is better not to meddle with the pendulum at
all, but to put the clock back by holding the scape-wheel
carefully for as many beats as may be necessary, if it is too
fast ; and if it is too slow, by first putting the hour wheels
forward by their adjusting work (150) and then stopping
the scape- wheel; and you may put the scape- wheel back the
time of two beats in one, if instead of merely holding it
steady you make it escape the wrong way. In regulators,
which always have a second-hand, the best way of retard-
ing the clock a few seconds is to put your finger firmly on
the seconds dial, just before the hand when it is deady so as
to stop it for the proper number of seconds. If it is less
than a minute too slow, you must first put the minute-hand
forward a minute, and then stop the second-hand.

260 GREAT WESTMINSTER CLOCK.

188. At this point the Westminster clock correspond-
ence begins to assume rather more of personal than of horo-
logical interest, of which however I shall divest it as far as
possible. But it is necessary to the understanding of the
matter to state that Mr. Vulliamy answered Mr. Barr/s
letter, enclosing these conditions, by declining to enter
into a competition, chiefly on the ground that he objected
to the astronomer royal as sole referee, because he con-
sidered other individuals as well, if not better qualified to
offer an opinion on the subject ; and secondly, because Mr.
Airy had shown himself prejudiced in favour of Mr. Dent,
by having publicly stated, through the Gresham Committee,
that he ^had no doubt the Exchange clock was the best
public clock in the world/ and in a subsequent letter of
March, 1847, to the same effect, he refers also to a letter
of Mr. Air/s to Mr. Dent, saying, ^ I shall state without
hesitation that I consider you the most proper person to
be entrusted with the construction of another clock of simi-
lar pretensions.^ On which it is obvious to remark, that
whether the recommendation, of a man to make a second
piece of machinery, because he had already made one of the
same kind to the satisfaction of his employers or their
referee (who had riot recommended him) is what is com-
monly understood by the word ^ prejudice,^ or not, Mr.
Dent had got no benefit from Mr. Air/s recommendation
that he should be employed, because the Board did not
adopt it; and he thenceforth stood in exactly the same
position as Mr. Vulliamy and Mr. Whitehurst.

In the- following month Mr.. VuUiamy sent to the
Board, through Mr. Barry, his drawings and specifications;

CORRESPONDENCE. 261

adding, however, that he had not prepared any estimate,
for the reasons stated in his previous letter on that subject,
and for the further reason that it would be useless, since
he had declined to make the clock under the direction of
the astronomer royal; and concluded by thanking Mr.
Barry for the very honourable and friendly manner in which
he had been treated by him throughout the business.

Mr. Vulliamy also, at the same time, availed himself
of Mr. Barr/s invitation to offer such suggestions as oc-
curred to him for departing from any of Mr. Air/s con-
ditions, and suggested a departure from no less than half
of them ; and, in fact, did not assent to one of them which
was not in accordance with his own previous practice. Mr.
Vulliam/s description of his own plans occupies 27 folio
pages; and therefore, though they might be interesting to
clockmakers, it is impossible to make any use of them here,
or, I may add, of the othqr specifications, descriptions, &c.,
on account of their length. Mr. Air/s opinion of them
all I shall have to state presently.

There was some farther correspondence about a card-
board model, which Mr. Dent offered to furnish by way of
illustrating hi^ plans, but which Mr. Vulliamy rightly said
was only throwing away time and money. In the letter in
which he declined to furnish such a model, he repeated his
objections to Mr. Airy, and added, that in several public
cases of reference of horological inventions the reference
was not to an individual but to a committee. Instead of
the card-board model, Mr. Vulliamy informed the Board
that he was then making for Mr. Feto a quarter clock of
rather more than one fourth of the size of the great clock.

^62 GREAT WESTMINSTER CLOCK.

and that he was purposely making it as like the great clock
as was practicable. I have myself seen this clock since it
was finished^ and it is a very handsome and well-executed
piece of machinery ; and in like manner the Exchange clock
might be looked upon as Mr. Dent^s models though not
intended to be exactly followed.

Various communications took place between Mr. Airy,
and Mr. Whitehurst and Mr. Dent, respecting the details of
the clock, and finally they both sent in their tenders, draw-
ings, fee, which were, together with Mr. Vulliam/s plans
and observations, submitted to Mr. Airy; and he also went
to make a personal inspection of Mr. Dent and Mr. White-
hursf s factories, and in May, 1847, reported to the Board
to the following effect. That as regards their factories and
tools, either of them, with some assistance from an engineer's
establishment for the large frame and the great wheels, is
competent to undertake the work. That Mr. Dent's expe-
rience, previously to his commencing the manufacture of
turret clocks when he undertook that of the Exchange, had
been chiefly in astronomical clocks and chronometers, in
which he had been compelled to pay the utmost attention
to the excellency of fine workmanship and to secure great
accuracy of results; and that since he commenced the
manufacture of turret clocks he appears to have entered in
an enterprising manner into that business, examining the
construction of foreign clocks of celebrity, and making
himself acquainted with the hterature of the subject. That
Mr. Whitehurst has had very considerable experience in
the manufacture of turret clocks, and is enthusiastically
fond of clockmaking ; but he has seen none but English

MR. AIRr's REPORT. 268

•

clocks, and those principally in a limited district. That if
it were necessary to entrust the making of the clock with-
out any control to one or other of them he should prefer
Mr. Dent; because he thinks it easier for him to acquire
Mr. Whitehurst^s solidity than for Mr. Whitehurst to
acquire Mr. Dent^s accuracy; but that under the most
trifling control, either of them will certainly construct the
clock in a perfectly satisfactory way. Lastly, he notices
the two estimates, which were, Whitehurst, £3373 ; Dent,
£1600. He says that it is out of his power to explain the
astonishing difference between them. It is not of much
consequence to the public what the explanation is; but
Mr. Airy suggests, first, that Mr. Dent may really be able
to do the work at less cost to himself than Mr. Whitehurst
(I suppose from his previous experience in the Exchange
clock) ; and secondly, that he may be willing to construct
the clock, even at a loss to himself, for the sake of the
reputation which he hopes to acquire by the makiug of
such a clock, while Mr. Whitehurst has made his estimate
at what is called a paying price. Mr. Airy (naturally
enough after what had occurred before) declined to offer
any further suggestion as to which of the two candidates
should be employed.

He added in a separate letter some remarks upon Mr.
Vulliamy^s plans and papers, as they had been submitted to
him by the Board with the others, although he considered
it impossible that Mr. V. could be employed to make the
clock, as he refused to comply with the proposed conditions.
He says that in regard to the provisions for strength, soli-
dity, power, and general largeness of dimensions, the plans

264 GREAT WESTMINSTER CLOCK.

•

are excellent ; but that in delicacy they fail^ and fail so
much that he considers that such a clock (except of course
as to its size) would be a village clock of very superior cha-
racter^ but would not have the accuracy of an astronomical
clock. The meaning of which is, that there are no provi-
sions in the clock proposed by Vulliamy for securing greater
accuracy of going, striking, or indicating the time, than in
a village clock of the ordinary construction but of superior
workmanship. With regard to the personal objections to
himself, Mr. Airy says that Mr. VuUiam/s demand for a
committee is not borne out by the instances he had cited;
because in all those cases the question was about the intro-
duction of principles, which if established were to be applied
to an infinite number of instances ; whereas here there is no
new principle : the instance is unique : its effects are only
those of the display of a good specimen of the present state
of the art : that (besides the similar case of the Exchange
clock) Mr. Airy is often requested by persons in want of
chronometers to recommend makers of them ; and, finally,
that Mr. Whitehurst, a bond fide competitor, had made no
objection to him as referree : in fact, he acknowledges
in his letters to the Board, that he had received valuable
information from the astronomer royal.

Since this report upon the plans in May, 1847, nothing
more has been done about the matter, except that on the
Board being reminded of their letter to Mr. Dent, Mr.
Barry was stopped from ordering any more of the smaller
clocks of his own authority, as he had done for the House
of Lords.

Many other remarks on the personal questions that have

EEMARKS. 265

been very unnecessarily introduced will have occurred to
the readers of the correspondence, or even of this abstract
of it ; but as they are of no importance to the science
of horology, I shall leave the reader to make them for him-
self. I will only add, for the information of those who
have no other means of knowing it, that none of the
gentlemen proposed by Mr. Vulliamy as referees have
given, to the public at least, any reason for believing that
they have paid any particular attention to the subject of
clockmaking, which, as to all the most important parts of a
dock, is a perfectly different thing from engineering. And
though I do not agree with the astronomer royal as to some
of the details of the plans suggested or approved by him, I
have no hesitation in saying that, unless his ^general condi-
tions^ are substantially followed, the clock will not be what
it ought to be, and what both the First Lords of the "Woods
and Forests have declared that it was intended to be. In-
deed, imless it is so made, it will be a mere waste of money
to make it at all, as there are plenty of clocks in that neigh-
bourhood for aU the ordinary purposes of public clocks,
though they axe of no use for the extraordinary purposes
for which this clock is intended, and is really wanted, and
which it will answer if properly made, but not otherwise.

It is satisfactory to be able to add that, if it is really to be
ever made, and made properly, there wiU be no reason
to regret the delay that has taken place, because in the
mean time some experience has been gained which wiU
enable a better clock to be constructed than that con-
templated in the plans which were settled three years ago^
and at quite as little expense.

266

ON PUBLIC CLOCKS.

189. The gratification of the curiosity of the readers of
this book on the subject of the Westminster clock was not
the only object of giving this history of it. I wish also to
point out to individuals and pubUc bodies who want to pro-
cure really good turret clocks a few things which they
ought to attend to^ but hardly ever do. Of course^ very
few such clocks as the Westminster or the Exchange clock
are wanted ; but as much as three or four hundred pounds
is sometimes spent upon a clock for a large town^ which is,
after aU, not eqnal to the cheapest ^regulator/ whicli may
be bought for 85 guineas. Instead of spending a large
sum of money upm such a clock, if not the best than can
be made, it would be in every way better to get a large
and strong clock for half the money, and a preUy good
regulator with it, and make the clockmaker who has the
care of it set it by the regulator every day if need be; or
what would be still better and cheaper, a dipleidoscope
(9), by which the clock can be corrected independetUlf
every day when the sun shines at noon. The truth is, that
what the astronomer royal said of the great dock may be
said with nearly the same truth of clocks very far short of
that in accuracy— *^ there is no market for such clocks.'
Plenty of clockmakers will contract for them and make
them, no doubt fairly and honestly enough as regards
the quantity of labour expended on them; but very few in*
deed,-*^o little demand is there for such things, — ^really
know all the particulars on which labour is worth expending,
and on which it is not.

PUBLIC CLOCKS. 267

There is a very sensible remark in one of Mr.VulKam/s
letters (whicli it was unnecessary to refer to for any other pur-
pose) to tlus effect that a great deal of superflnous work is often
expended in polishing parts of the clock which have nothing
to do, as indeed I have already noticed in § 181. But it
requires some boldness in a clockmaker to omit these
things, for nine people out of ten who go to look at
a clock judge of its goodness merdy by its finish (which in
small work, especially watches, is generally not a bad test,
by a sort of convention among the makers) ; and even the
tenth person, though he may be aware that the going of a
clock does not depend on the lacquering of the brass or the
polishing of the ironwork, does not know what it really does
depend upon. How many people, for instance, know
whether a scape-wheel ought to be light or heavy —
whether the teeth ought to fall very near the comer of the
pallets, or a good way up on the dead part— whether
a pendulum is better fixed close behind the pallet-arbor, or
on some convenient part of the wall at the side of the
dock — ^why some clocks will go very well with short pen-
dulums, and others go much worse with long and heavy
ones— whether cast iron cams on the great striking wheel
cause more or less friction, and more or less waste of power
than polished steel pins on the great wheel or on the second
wheel— and why in one case cast iron wheels will act with
less ftiction than cut brass wheels in the other case-and
so forth ?

There can be little doubt therefore that for obtaining
a really good public clock, such as most large towns have
paid for, whether they possess it or not, the only safe way

N 2

268 PUBLIC CLOCKS*

is to go to some one^ or at the most some tliree or four
makers of the first reputation^ and adopt the clock which
is proposed by the one whom you ultimately select, either
with reference to their price or other considerations. Of
course the more ordinary the clock is required to be, the
larger will be the number of persons competent to make it.
And where tenders are obtained, from any but snch a select
number of makers, as I have just now supposed, it is espe-
cially necessary that the advice of some competent person
should be obtained either as to the conditions to be ob-
served, or as to the character of the clocks usually made
by the persons proposed to be employed, as there is always
a strong family resemblance between the clocks of the same
maker.

190. With regard however to testimonials respecting
clocks I must caution churchwardens and others to whom
they are sent, that they are (like all other testinK)nialB
nowadays) in many instances most fallacious, being fre-
quently given by persons who have no means of ascertaining
the real rate or the real value of the clocks about which
they testify, and who are quite incompetent to fonn aiL ac- j
curate judgment of the construction of a clock. Two
opposite instances occur to me, as illustrations of the Talne
of testimonials of this sort. I have seen a printed tes-
timonial about a clock, to the effect that it had not varied
five minutes in several months. Now such a tesdmoiiial
is not worth five farthings ; for it may have meant, eith«
that the clock had a steady gaining or losing rate of twc
or three seconds a day, which amounted in several monthf
to five minutes; or that it was never more than two nunutei

TESTIMONIALS. 269

too slow or three minutes too fast; or (what was probably
the &ct) something between the two : in the first case the
dock was a very good one; in the second case it was a
very bad one ; and in the third it may have been anything
between those two extremes. On the other hand, I heard
of a clergyman in London being asked the character of a
clock that had been made for his church by an eminent
maker, and he replied that it went very ill : this came to
the ears of the person most interested in the matter, who
from his own or his men's periodical observation of it
thought it deserved a much better character, and he re-
quested the clergyman to inform him by what standard of
time he was in the habit of trying it ; and he replied, ' by
the clock of the principal church of the parish.' And it
being thought by those who had made the original
inquiry that the clocks of chapels of ease are not bound
by ecclesiastical obedience to the mother church, and other
inquiries proving satisi^tory, the maker of the contu*
maeious clock was employed Upon the business in question.
I can give one hint on this subject which may be useful,
viz : that any testimonial about the going of a clock for
so many months ought to extend from winter to summer,
or it is of no real value.

191. With regard to clocks of what be called the
second degree of excellence, or, as we may for convenience
call them, village clocks, there is of course not quite the
same necessity for caution as to the admission of can-
didates. At the same time nothing can be worse than
the common practice of churchwardens, government offices,
and public bodies, of issuing a notice that a clock is re-

B70 PUBLIC CLOCKS.

quired to show time on a face of such a size, and to strike
on a bell of such a weight, to go eight days, all the wheels
to be of the best brass, and several other best things, and
that tenders must be sent in by 12 o'clock on sach a day^
the only condition they seem to consider of iniportanoe.
I said nothing can be worse ; but I belieye there is one
other worse method, which I lately heard of hdng adopted
by a certain town council, who after spending several
thousand pounds on new markets, naturally thought that a
small clock on the building would be useful to those who
frequent it : go to some respectable maker and ask what he
will make the clock for ; then take his estimate about to
other persons and inquire for how much less ihej will do
it. In this way you may make sore of getting a dock 25
per cent, cheaper and 50 p» cent, worse than the original
estimate.

As an illustration of the results of the system of ten-
dering without a detailed specification, I may be allowed to
relate an anecdote in which I was accidentally concerned
not long ago. I was staying at a place where the in-
habitants were about to put up a church dock; and it
being known to the clergyman that I took some interest in
such things, I was requested to attend, as a sort of as-
sessor, at a parish meeting at which the selection of the
maker was to be determined. They had received six or
seven tenders, varying in amount from £60 to 100 guineas ;
and it appeared that several of those who had sent in
tenders also proposed to tendesr themselves to give any in-
formation that might be required by the meeting. The
parishioners said they did not know what information to

TENDERS. 271

ask for ; all the candidates offered to make the best pos-
sible clocks and several of them had sent testimonials
equally good as to their capability. It appeared therefore
that the only way in which I could help them was to en-
deavour to ascertain from the clockmakers who were in
att^dance what kind of clock they really intended^ and
were able to make. The result was (as I afterwards
heard)* that two of the candidates^ who were prepared for
an examination by the vestry^ declined the examination by
their assessor ; and also that* I had no difficulty in deciding
that the intended clock of one of the two who did appear
would be dear at any price^ and in selecting another as
competent to do the work^ and intending to do it in such
a manner as would be creditable to himself and satisfactory
to those who had to pay for it; and he agreed to make it
according to certain conditions which I was to famish him
with. I have lately had an opportunity of seeing the
clocks and I was glad to find my selection justified by the
result. Of course I do not mean to say that some of the
other makers who sent in tenders^ but did not come to the
place^ might not have done it just as well; but I relate
this anecdote to show that out of six or seven persons who
all professed to make a clock with everything of the best
quality^ there were at least three who were either not able
or did not intend to do what they promised^ and yet were
just as Ukely in the common course of things to have been
employed, as the person who was employed ; in fact more
likely, because his tender was very nearly the highest.

The truth is that the persons who prepare what they
call the ^ecificatian for a public clock generally do not

272 . PUBLIC CLOCKS.

know any more than any man in the street what ther
really want^ or ought to want : they know the remit they
want^ if they have a bell or a clock face ready made^ but
nothing more. And it is quite a mistake to impute dis-
honesty to any clockmaker^ merely because he sends in
either a very high tender or a very low one ; for until they
are examined by some competent person^ there is no means
of knowing whether the clock which each of them proposes
is not really a fair clock to make for the money he ssks ;
and one is just as much in conformity with the specifica-
tion, which specifies nothings as the other. And the prac-
tical result is, that the best makers will not take tde
trouble to tender, as they are sure to be underbid. Every
now and then the architect tries his hand at the clock spe-
cification. But even architects are not omniscient. I have
seen a specification — ^and a second explanatory specification
too — ^furnished sometime ago by an eminent architect for m
important public clock, which, if it had been printed instead
of shown to me in manuscript, I would have copied here,
not the least by way of any reflection on the gentleman who
wrote it, but by way of showing how necessary it is that
the public should resort to some better way of securing a
good clock, than putting it into the hands of the architect.
192. Still the question remains, how are people in
ordinary circumstances, who want as good a clock as pos-
sible for the money they can afford, to proceed to obtain it.
If the clock is really intended to be a first-rate public time-
keeper, such as all large towns ought to have, I have
already mentioned what appears to be the only safe way of
obtaining it. And I may add, that I believe there are few

CHURCH CLOCKS WITHOUT DIALS. • 273

towns in the kingdom of 10,000 people, in which there
are not to be seen a number of clocks on different public
buildings, which, even when they do not all set up for
themselves, only keep among them a sort of conventional
time, quite distinct from any of the known descriptions of
time, sidereal, solar, or mean, Greenwich, . or local time.
And the money spent* on aU these bad clocks would have
suiBced to procure one as good as can be made, and strik-
ing so as to be heard all over the town, and from which
any number of comparatively cheap dials (or silent clocks)
might be daily regulated, if necessary. Indeed it should
be remembered more frequently than it is, that the strikmg
of a public clock is what people really go by, and set their
own clocks by. There are many places in which it would
be better, both on account of the architecture of the church
where the beUs are, and its position, to put a striking
clock without any external face (which moreover gives it
considerable advantages in going) in the church, and to
put a large dial in some other more conspicuous part of the
town. Peterborough and Lichfield cathedrals, and several
handsome churches which I could mention, are not defaced
with visible dials, there being no sufficiently large space of
blank wall on the bell towers on which dials could be
placed. And the money that dials would cost, including
the extra work they frequently require in the clock, may be
much more profitably spent upon quarters, which ought to
be more frequent than they aire.

193. It appears to me that where the churchwardens
have no better means of obtaining assistance, I may pos-
sibly make this book worth the two shillings it will cost

274 ^ ADVICB TO CHUBOHWABDENS.

them, if I conclude it with some hints as to the conditioiis
or tenns which they ought to require those who send in
tenders for a dock to observe or to specify; making them
in fsud, or such of them as may be finally adopted, a portion
oi the contract with the clockmaker, and also affording the
means of comparing one tender with another. And tiie
maker may be required to submit to the judgm^it of some
person conversant with machinery, whether the conditions
have been properly observed, before he is paid.

On the subject of the pendulmn, and indeed on all
other matters here mentioned, I must refer to my re-
marks in the earlier part of this chapter. As it is a mere
question of money whether the pendulum should be
compensated or not, the purchasers must deitermine it
for themselves. If the pendulum is as much as 8 feel
long (which nearly every place will admit of), the bob
should not be less than 1^ cwt; and a 14 feet wooden
pendulum may as easily have a bob of 2 or S cwt. as a
lighter one, as there are no compensation tubes. A zinc
compensation tube should be required to be made as de-
scribed in § 132, at least until some method is found of
rolling ziQC tubes thick and solid enough for this purpose.

If the pendulum is not compensated it must be of
wood, either deal or mahogany, straight in the grain^ and
well varnished, and of the thickness before mentioned (see
§ 138 and the following ones).

The escapement to be what is technically called half-
dead (38), and the pin-wheel escapement (46) to be pre-
ferred.

The frame to be of cast iron, the maker to state of what

CONDITIONS. 276

thickness^ and also the general construction and size of it :
it being an express condition that the main body of it
should never require taking to pieces for cleaning the clock
when once fixed (136).

State how many days the clock is to go^ and whether
each train is to have three or four wheels, with reference
to the circumstances mentioned in § 189, &c. In all cases
a three wheeled train to be preferred, and the striking is
to be from the great wheel, especially in large clocks,
unless for some special reason it is impossible ; and de-
scribe the cams or pins and lever arrangements.

The pallets, and all the wheels, except the great ones,
in each train are to take out separately; or it will be suf-
ficient with respect to the wheels next above the great
wheels if their bushes take out so that the wheels and
pivots can be cleaned.

The barrels to be of strong sheet iron brazed together,
and, if possible, of such a size that all the available fall can
be used for the weights hung by a double line ojily : if
however this would make the barrek smaller than four
inches in diameter for a small clock, and five for a lao^
one, there may be three lines."**" •

The number of leaves in all the pinions to be stated,
and of course high numbers to be preferred, except that if
lantern pinions with steel pins are used, the numbers may
be one-third kss than those of leaved pinions. The great
wheel of the going part should not have to drive fewer

* It must be remembered that the diameter of the barrels must
be less than that which appears by oalcnlation to produce a certain
fall, by an amount equal to the thickness of the rope.

276 ADVICE TO CHURCHWARDENS.

tban 16 leaves^ and the higher wheek in the train 12. If
the striking is done by the second wheel, its pinion should
not have less than 16 or 18 leaves; if not, 10 or even 9
leaves will do.

The size and thickness of the great wheels to be stated,
and the size and number of teeth or pins of the scape-wheel.
If the great wheels turn in three or four hours a foot
in diameter is enough in ahnost any case for the going
great wheel, and 1^ for the striking great wheel, each being
about an inch tliick. If they turn slower, they must
be* larger, in proportion, for large clocks.

State whether you intend to use brass or gun-metal : if
brass, aU the wheels to be hardened by hammering.

State what kind of maintaining power you intend to
apply, the preference being given to Harrisons's going
ratchett, unless the bolt and shutter is made as described in
§ 159.

State the size of the bevelled wheels in the leading-off
work, if any; no rule can be laid down for them, but they
ought to be from about five to nine inches in diameter,
according to the size and number of the dials; those be-
longing to each dial (if mote than one) need not be so thick
as those that work the whole : see § 149. These wheels
may be of cast iron.

All the wheels and pinions of the dial work to be of
brass, to prevent rusting. In all other parts of the clock
the pinions to be of steel (not iron case-hardened) (152), and
the pivots also.

Describe the dial you propose, if it is not already pro-
vided; the hands to be as described in § 155.

CONDITIONS* 277

If there are quarters on two bells^ the striking wheel to
be like that of the hour, with pins or cams alternately on
each side; and in both parts the levers are not to have their
axis between the striking pin and the wire (167). If the
quarters are on four beUs, see § 168. State whether the hour
is to be Ifet off by the quarters or the going part : the latter
in very accurate clocks is the best, but requires rather more
force in the going part.

The hammer-shanks and tails, and cranks, to be l8
inches long at least, where the position of the bells allow it;
and as few cranks as possible to be used, and all the pivots
to have brass bushes.

State the weight and rise of the hammer-head from the
bell, and the weight and fall of the striking weight with
which you intend to obtgon that rise (165).

There must be an internal regulating dial for minutes,
adjustable by some such method as described in § 150,
according to the size of the clock ; and either a small hand,
or a visible mark on the scape-wheel with a fixed index, to
examine the going of the clock to seconds, if it is intended
to be a very good one. The regulating dial to be visible (if
desired) through a glass in the clock-case.

The whole to be enclosed in a wooden case, which can
be opened on all sides, but locks up securely, leaving the
winding holes open,* so that the clock can be wound with-
out opening the case. The pendulum also to be enclosed,

* In regulators (house clocks) the winding holes are frequently
made in the glass, with brass caps, so that the case never requires to
be opened, and moreover servants can then safelj be left to wind up
the clock without the possibility of their meddling with thq hmls.

278 ADVICE TO churchwardens;

and where it is in a light place, a glass may be placed near
the bottom to see the degree plate through. The weights,
if required, to be boxed off for safety, and provisions to pre>
vent accidents to be made where necessary (184).

On the other hand, the clockmaker may fairly demand,
in order that justice may be done to his dock when it
is made, that the chamber in which it stands shall if
possible be made so light that a candle shall never be
required to examine the dock in the day time; otherwise
the clock will never be properly cleaned.

And it is equally due to the maker of a good clock, as
well as for the interest of those to whom the dock bdongs,
that a competent person should be employed to examine and
dean it periodically ; who will probably w>t be the person
who undertakes to do it for the least money. Some of tiie
readers of this book wiQ know of a town which had to pay

rather dearly for putting its church dock into the hands of
a cheap and ignorant contractor; for having to do some-
thing to the hammer, he leffc it striking with its edge instead
of its face, and thereby cracked a very fine bell of 30 cwt.

I do not propose the above conditions as perfect, or as
necessary to be imposed upon clockmakers who from their
known character can be trusted to do without. But I
believe that few such clockmakers would desire to make
any material alteration in them, as they by no means restrict
them to any particular pattern of clock, and are in a great
measure adopted from the practice of the best makers. And
I have no doubt that such makers would rejoice to see
some such test applied to themsdves and their competitors,
as it would certainly tend to exclude from our churches and

CHURCH CLOCKS. 279

public buildings many pieces of machinery, which not only
are a disgrace to them, but also discourage all attempts to
improve the art; since no one will go on spending his time
and money in contriving and making improved machines
which are to be rejected for old fashioned and good for
nothing articles made at somewhat smaller cost.

I shall be glad if this, the only English book on the
construction of Public Clocks, does anything towards raising
the character of a machine, which, notwithstanding its ge-
neral and important uses, has been strangely left; behind in
the progress of mechanical improvement ; and which, not
only in its history but in its own duration, connects the
present with the past more than any other instrument in
use : a machine of which it has been happily said,"^ 'there
is no dead thing so like a living thing as a dock :' delibe-
rately performing its appointed work by day and by night,
with scarcely any interruption during the lapse of many
generations of men, reminding them aR of thL own pass-
ing away, and of the period when 'the great clock of Time
will have ruQ down for ever/

* In ' The Old Church Clock/ by the Rev. R. Parkinson, Caaon of
Manchester, a pleasing little book, but not on dockmaking.

THE BKD.

08TXLL, PB.XVTXR, MA&T 8TBXST, BLOOMBBVRT.

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